Pros: Can hit 3.5 GHz rock solid stable (YMMV), low FSB and high multiplier (easier OC)
Cons: Bad heatsink mount design, high temperatures (even at stock settings)
The bottom line: The Q6600 G0 stepping represents the current sweet spot for price and performance. Just need better cooling.
It's no secret that Intel's current Core microarchitecture is superior than AMD's current K10. It is also no secret that Intel was ready to unveil a 45 μm refresh of the Core. The quad-core version would be codenamed Yorkfield. Not only will the die be smaller than today’s quad-core (codename Kentsfield), it would also include a new SSE4.1 instruction. All in all, when tested, many respectable review sites say that the Yorkfield performed faster than the current Kentsfield quad-core CPUs even at the same clock rate.

Oh yes, but thanks to the new Yorkfields, the prices of the Kentsfield came down. In fact, Microcenter had the Q6600 G0 stepping of the Intel Core 2 Quad CPU on sale for $199. Fry’s had it on sale for $189 for a brief moment. Both a good deal since many stores still sell them around $250 or so. Plus, there are many experiences with overclocking the Q6600 so it is a very robust and stable core to play with.

One Over The Other
So why did I decide to go for the Kentsfield (Q6600) instead of the new Yorkfield (Q9300) version? Or rather, why should you do the same at this point in time? A couple reasons, really.

Multipliers and Front Side Bus (FSB)
The Q6600 have a high multiplier of 9x. This allows for faster CPU clock rates while keeping the FSB more relaxed. The FSB of the Q6600 is 266 MHz, which gives the overclocker more headroom to push forward. Stock settings are 9x 266 MHz = 2400 MHz (2.4 GHz).

The high multiplier of the Q9300 is only 7.5x. The new Yorkfield CPUs also ride on a faster FSB (333 MHz vs 266 MHz). This means that not only do you start with a lower multiplier, you start with a faster FSB. Great for non-overclockers, but it’s a limitation for people who want to push it to the limits. Stock settings are 7.5x333 MHz = 2500 MHz (2.5 GHz).

For overclocking, the Q6600 is simly more flexible.

Price
The cost of the Q6600 went down with the release of the consumer-level Yorkfields (like the Q9300). While the Q9300 is pretty affordable for a quad-core ($280 at Newegg last I checked), you can find the Q6600 for much less (bought mine at Microcenter for $199, found a sale at Fry’s for $189). The performance difference is small. Sure, the Q9300 is slightly faster, but the $80 difference really isn’t worth that increase.

Proven Mature Process
The good old 65 μm process has been around for a while. The 45 μm just started it’s life. While 45 μm gives hope to higher clock speeds, we won’t know until some brave soul decides to push it to the limits. Currently, the Q6600s are known to hit at least 3 GHz at without touching the voltage settings. In fact, most can do 3 GHz with Intel’s SpeedStep turned on.

A small voltage bump allows for even higher CPU speeds. Most can comfortably at 3.4 GHz with a reasonable voltage bump. Others can do 3.6 GHz, but may require crazy cooling contraptions as well as needing more voltage.

Cache Size
Actually, if both the Q9300 and Q6600 are clocked the same, the Q9300 is still slightly faster than the Q6600 despite the fact that the Q6600 have a bigger 8 MB of cache. The Q9300 makes do with only 6 MB, 2 MB short of the older Q6600.

While the cache size doesn’t seem to hurt the Q9300, bigger can still be better in certain kids of applications. I call this a draw.

In the Box
As with most Intel retail boxed CPUs, the package is simple – you get an Intel heatsink/fan combo along with the CPU itself. A small booklet shows how to mount the CPU as well as the limited warrantee in multiple languages is also included. The “Core 2 Quad” sticker is affixed on a piece of wax paper which is stuck on the booklet as well. This allows you to show to the world that you are sporting a Core 2 Quad inside of your PC.

The CPU and heatsink/fan combo is housed inside molded plastic that are fused together to form a safe cocoon for the product. Just be careful tearing it apart. Too much force and the CPU along with the heavy heatsink can fly away from you. It doesn’t feel very good when your brand new CPU hits the floor. It feels even worse if the heatsink hits your bare foot.

Installation
Installing the CPU into my Gigabyte GA-P35-DS3L rev 2.0 motherboard was a snap. You just lift the lever and the latch, place the CPU into the socket, and then fold down the latch and then the lever. This holds the CPU down in place.

Installing the heatsink was pretty easy, too. The thermal paste was pre-applied to the heatsink base from the factory. Just line up the bracket and push in the pins.

Installing aftermarket heatsinks is a different story. Thanks to the large size of most aftermarket heatsinks and the placement of the pins, it is hard to get access to them. This is especially true when the motherboard is already installed inside a case.

Removal of the heatsink will require you to have a flathead screwdriver. All you do is take the screwdriver to the plastic posts and twist to pop the pins up.

Overall, the plastic pins and post are not as durable as previous mounting methods used by AMD and Intel’s own Socket 478 CPUs. The plastic posts are easy to snap off, and with repeated uninstalls and reinstalls, the plastic tabs will wear out. In fact, a few wore out on me.

Overclocking
While the standard 2.4 GHz clock speed will satisfy most people, I love being able to squeeze out as much performance as I can from relatively inexpensive parts. This is what compels some of us to bolt on turbochargers onto factory 4 cylinder engines, is it not?

Many people have reported that they can do at least 3.0 GHz at the stock voltage of 1.325v. Some can do 3.2 GHz. And some can only muster 2.7 GHz or so.

I went through 3 different Q6600 CPUs myself. The first one was decent, posting a 3.2 GHz at stock voltage. Bumping it up to 3.33 GHz required another .025 volts. I didn’t get to use test this CPU since it a client wish to build a new PC and wanted the CPU. I figured I could sell this one and buy myself another one.

The 2nd CPU didn't fare as well. I was only able to get 3.0 GHz at stock voltage. 3.2 GHz required another .025 volts, while 3.33 GHz required an additional .05 volts. At 3.33 GHz, temperatures were soaring high above 60c! I used an aftermarket cooler (Arctic Cooler Freezer 7 Pro) along with some good thermal paste (Arctic Silver Ceramique). Getting to 3.4 GHz was proving to be difficult, so I sold this one on eBay and actually made a few bucks.

The 3rd CPU fared better than the last two. I was able to hit 3.2 GHz at the stock voltage, which was 200 MHz faster than the 1st CPU I had before. Pushing to 3.33 GHz required only 1.35v. 3.4 GHz was possible at 1.375v. 3.5 GHz was good at 1.425 volts (a jump of .05v!). 3.6 GHz proved hard to attain. I was not able to get any Prime95 stable results at 3.6 GHz with voltages up to 1.5v, which is the highest I feel safe (at least for short term testing).

Even with an upgraded heatsink and fan combo, the Q6600 is a very hot CPU! Using stock settings and voltages (including SpeedStep), idle temperatures (1.6 GHz) was sitting around 40c! Under Prime95 stress testing, load temperatures (2.4 GHz) soared to 61c! I thought that the temperatures were wrong, but according to my research, CoreTemp (an application that reports CPU temperatures) is pretty accurate. Overclocking at 3.5 GHz (the max stable I attained) pushed the CPU as high as 70c, but sometimes briefly hitting 80c! The only way to keep it stable at 3.5 GHz required me to leave the side panel of my Antec Lanboy case open.

I've tried to reseat the heatsink a couple of times, but each and every time the temperatures were consistently high. I will try the stock Intel heatsink/fan combo and report back. I also ordered a heatsink lapping kit to see if that helps with the temperatures. Lastly, I have a Thermalright SI-120 heatsink I used for my old S939 set up that seems beefier than the Arctic Cooler Freezer 7 Pro. I also ordered the bracket to use this heatsink on a LGA775 CPU, so we’ll see if that helps as well. Otherwise, I’ve heard really good things about Thermalright Ultra 120 Extreme. However, I’m trying to avoid having to spend another $60 for another heatsink if the one I own works well enough.

I hope to see the temperatures will drop when I lap the heatsink or change it over to a Thermalright SI-120. This may also help me get to the 3.6 GHz mark.

UPDATE: So I went ahead and started my process to return the Arctic Cooling Freezer 7 Pro heatsink fan. I had to use the stock Intel heatsink/fan that came with the Q6600. I put all settings back to stock speeds and voltages, and guess what? With the side panel off, the CPU sits at 1.6 GHz on 1.16v but produces 40c of heat! When all 4 cores were loaded with Prime95, it went up to a whopping 71c! With the side panel on, it idles at around 48c, and loads at 80c! I guess the Q6600's heat output is normal if Intel's own HSF allows for 80c loads. I don't feel very comfortable knowing it was running this hot, however. Re-seating the stock HSF did not improve temperatures. There were 2 cores that was running between 4-8c cooler than the others.

Oh, and the VID for this particular CPU was 1.25v (the previous one was 1.325v). I found out that not all Q6600s have a single default "stock" voltage, and Intel seem to set it what they deem right for the particular part. The VID tells your motherboard how much voltage to give it.

Performance
I have yet to perform any formal benchmarks, but using PCMark05, I tried to gauge the relative performance from stock to the different levels of overclocked speeds. Jumping from 2.4 GHz to 3.2 GHz yielded the most performance gain. I was shocked, however, to see that jumping from 3.2 GHz to 3.5 GHz didn’t have that leap of performance I was expecting. It was minuscule at best.

If you can’t get any higher than 3.2 GHz on your Q6600, don’t worry about it!

Power Consumption
Here’s the parts list of my rig:

Gigabyte GA-P35-DS3L rev 2.0 motherboard
Intel Core 2 Quad Q6600 G0
Arctic Cooler Freezer 7 Pro (heatsink/fan)
Patriot DDR2-800 2 GB (1x 1GB sticks) memory at 4-4-4-12 timings (2.2 volts)
2 Western Digital Raptors at 34 GB each (RAID0)
JMICRO PCI-E controller (for the Raptors in RAID0)
Seagate 500GB SATA drive
MSI Geforce 8800GTS 512 MB video card
Seasonic S600 600W PSU

They are all wrapped up in Antec’s light Lanboy aluminum mid-tower case. Power consumption was measured with a Kill-A-Watt power meter.

At the stock 2.4 GHz with SpeedStep (idles at 1.6 GHz), the entire rig sucks up 145 W. Not bad for all those components as well as a quad-core CPU. Running Prime95 with all 4 cores loaded, power consumption rises to a respectable 225 W.

Repeating the test at 3.2 GHz (SpeedStep disabled for all overclocks) yielded an idle power consumption of 175 W. Loaded, the entire rig ate up 245 W. Still not too bad.

At 3.33 GHz, as expected, power consumption didn’t rise too much. 180 W idle, 250 W loaded.

3.4 GHz yielded 195 W idle, 275 loaded.

3.5 GHz ate up 210 W idle, and 300 W loaded!

Last, but not least, the very unstable and hot 3.6 GHz clock speeds was at a whopping 230 W idle, and 330 W loaded!

Power consumption goes up exponentially after 3.33 GHz! It’s not too surprising if you read the above voltages required to keep the CPU stable at higher speeds.

Conclusion
The Q6600 G0 stepping CPU is a highly overclockable if you get the right core. Even if you don’t, the worst overclockable Q6600 can still hit at least 3.0 GHz at stock voltages. Along with the price drop, this makes the Q6600 more desirable than ever before.

The temperature of the Q6600 is shocking, however. Even when SpeedStep lowers the clock speed to 1.6 GHz and voltages drop to 1.16v, the temperature still will not go any lower than 40c! With all 4 cores loaded, even with a highly respected heatsink/fan, the temperature soars to 60c! Overclocking can net you temperatures over 70c!

Despite the high temperatures, I was able to keep the CPU overclocked (albeit with the side panel of the case left open) at 3.5 GHz, which goes a bit above 70c, with Prime95 running for over 12 hours.

The only other negative is the power consumption. While it’s not a green CPU, it’s respectable for a quad-core at stock speeds and voltages. However, once you disable SpeedStep and start cranking up the speed and voltages, power consumption rises exponentially.

It’s a great CPU for bragging rights, as well as brief computational-heavy projects. It’s also great for next-generation games. It’s not something you’d want to keep on 24/7 unless you can afford the bills and can stand the glares from environmentalists. All in all, if you were looking at a quad-core CPU, you already knew what you were getting into in the first place. If you just need all the CPU power you can get at a low price, the Q6600 represents that sweet spot for price and performance.