System Builder Marathon: Overclocking

Overclocking the Sub-$2000 PC

Armed with our Swiftech H20-120 water cooler, we had high hopes for our mid-range system. We thought we’d be able to get close to 3.7 GHz, but unfortunately fate and circumstance got in the way.

You see, the Q6600 CPU we used for the marathon is somewhat older and not part of the overclock-friendly G0 stepping family. Even though our first overclocking attempts were positive—with water cooling, the CPU would boot and pass memtest at 3.6 GHz—the fourth core would consistently fail Prime95 after about 18 minutes. Regardless of the voltages we used, this problem refused to go away, so we had to set our sights lower.

At the end of the day, we had to settle for a rock-stable 3.42 GHz. While this is slightly more than 1 GHz over the Q6600’s stock speed of 2.4 GHz, we were a little disappointed. How much did our liquid cooling system help ? On air cooling, this older CPU maxed out at 3.12 GHz in a previous test, so at a cursory glance it seems to have provided us with a respectable 200 MHz increase in conjunction with lower temperatures. A newer G0 stepping Q6600 would very likely upped the ante to the 3.7 GHz neighborhood, and maybe a little more.

At its overclocked 3.42 GHz clock speed, the current system builder marathon machine will be facing the previous Q6700-equipped mid-range system that overclocked to 3.6 GHz thanks to the newer stepping. Even with this 180 MHz clock deficit, we think the results will be fairly close, and we expect the new system to obliterate the previous system when it comes to gaming, as it is equipped with two video cards in an SLI configuration. The overclock should prevent it from being held back by a low CPU clock speed, shifting the bottleneck back to the video cards.

Speaking of the video cards, we managed to overclock both of those, too. Of course when overclocking SLI’d video cards, they have to both be running at the same speed, so overclocks are limited to the lowest common denominator. Even so, we managed to push the cores to a 9800 GTX-beating 710 MHz. The video memory wasn’t as agreeable as we’d hoped, peaking at 1025 MHz, but these gains will still show real results in the benchmarks.