Assembly And Overclocking
The best assemblies are the ones where I don't have a lot to talk about, which means that things have gone smoothly. This is one of those builds. The Cooler Master CM 690 case provides a lot of space and decent cable management, so there isn't much to talk about on that front. Even the large Radeon HD 5850 cards have a lot of breathing room. Indeed, all of the hardware and software installations went off without a hitch.
Overclocking this beast was simultaneously disappointing and impressive.
Let's start with the disappointing stuff: we had a heck of a time getting any stability past 3.7 GHz, even though the Rosewill Fort 120 cooler was doing an awesome job keeping the CPU temperatures down. While the system didn't have a problem booting over 4 GHz, running a Prime95 stress test would crash it fairly quickly. With load temps under 75 degrees Celsius, we were surprised that upping the voltage didn't help. If anything, it seemed to crash faster. Further testing confirmed that it was actually the extra voltage that caused the crashes.
After discovering the extra-voltage limitation, we got to the impressive part: with some more tweaking at stock voltage, this Core i7-920 CPU remained stable all the way up to 3.9 GHz. With the voltage this low, even a Prime95 load test resulted in CPU temperatures below 70 degrees Celsius (an extremely low result for an overclocked Core i7). Our target with a reasonable voltage increase was a stable 24/7 overclock in the 4.1 GHz neighborhood, so 3.9 GHz isn't a terrible trade-off, considering the low power usage and temperatures. A 1,233 MHz overclock at stock voltage speaks to the success of the Core i7-920 D0 stepping.
As far as the graphics cards are concerned, PowerColor's Radeon HD 5850 cards overclock to the maximum Overdrive limits in the Catalyst Control Center (CCC) without any extra effort. These cards could probably go further than the 775 MHz core and 1,125 MHz memory limitations built into their BIOS, but since we're running these in a CrossFire configuration and want to keep things as stable as possible.