Assembly And Overclocking
This system was well thought out during the planning stages, and it really paid off with a smooth, clean assembly. The NZXT Tempest affords a lot of space, and the graphic cards weren't even difficult to fit together in MSI's well-placed PCIe slots.
Our only complaint--and it's a nitpick, really--is that the Gigabyte GV-R485OC-1GH graphics cards didn't come with CrossFire cables, which is a shame since they are premium Radeon HD 4850 offerings. While MSI thoughtfully included two cables with the motherboard, three are necessary for quad-CrossFire usage, so we had to use an extra one we had lying around.
Other than that, we have absolutely nothing to report. Everything ran smoothly on first boot and the Catalyst Control Center (CCC) was happy to utilize all four cards in CrossFire. With such a fringe setup, we assumed there'd be a bit more to do, but no fiddling was necessary.
Overclocking was a bit more involved. The graphics cards bombarded the case with heat, since these Gigabyte Radeon HD 4850s don't push their hot air out of the back of the case. The Xigmatek CPU cooler thus had to earn its keep.
The system would boot to 4 GHz, but the CPU really wanted a lot of voltage to get there. Of course, voltage begets heat, and heat begets instability. I suspect if the graphics cards exhausted their heat out the back of the case, or if we'd have had some liquid-CPU cooling, our overclocked numbers would have been a lot more impressive.
At the end of the day, with 1.46V fed to the CPU, we found a balance of speed and heat at a reference clock rate of 245 MHz and at the stock 15x multiplier, we were able to settle on a stable clock speed of 3.675 GHz. This is nothing epic, but is not terrible for a 24/7 overclock.
In order to keep memory latencies low, we had to choose a ratio that gave us a slight memory underclock to 1,306 MHz, but still allowed us to maintain the 7-7-7-20-27-1T timings. We also lowered the HyperTransport link multiplier to 9x, and the CPU-NB link to 8x. Northbridge voltage was increased slightly to 1.3V, and ACC was set to “Auto.”
The graphics cards were completely unwilling to budge at all in our overclocking efforts. While this is unfortunate, it's not entirely unexpected as the cards have a high factory overclock, meaning less headroom right out of the gate. We're also dealing with four cards in CrossFire, and the environment is not ideal for overclocking. On the positive side, these four Radeons are powerful enough to be held back by the CPU speed, so the CPU overclock should show us some positive gains.