Utilizing the Auto-Tune feature built into the Catalyst Control Center, we got a baseline overclock of 978/1390. Although this passed CCC testing, it could not hold up to Furmark, and crashed almost immediately under load. After further tweaking, we found the max stable clocks at the default 1.212v and Auto fan control to be 959/1353. That's a 10½% increase from the already overclocked 868MHz core frequency (nearly 13% over reference) and 12½% more on the memory. By bumping the core voltage to 1.25v and using the SmartCooling feature of ASUS SmartDoctor to speed up the fan, the core could be further increased to 975MHz. Unfortunately even the "Slow" speed setting on the fan results in a high amount of noise, and at the "Fastest" setting it literally sounds like a hair dryer running at full blast inside the case. While probably acceptable for benchmarking, I found the noise intolerable even gaming with over-the-ear headphones on.
Using a Kill-A-Watt meter I measured total system load to be right around 100W at idle, and up to 283W stock, 310W overclocked under Furmark GPU load. According to ATI a reference 5870 should consume 27W at idle and up to 188W under load, so it appears our ASUS 5870 V2 is very close to where it should be as far as power usage goes.
Temperatures for the card averaged less than 40° C at idle and not quite 80° C under Furmark GPU load with the fan left on Auto control. This varied between 21% and 33% fan speed, or roughly 1000 to 2000rpm, which was barely audible outside the computer case. Using manual control, the fan can be adjusted up to nearly 4300rpm, however as mentioned previously anything above 50% is simply impractical for normal use. Although we don't have a reference 5870 card to compare to, going by other reviews it seems that the ASUS 5870 V2 cooler may yield 5° to 10° lower temperatures than stock, which lends credibility to ASUS' claims of 17% better cooling.
While I was using Furmark to perform stress testing for both stock and overclocked modes, and determine temperature and power usage for the card, I recorded the scores obtained from the benchmark runs. In this and all following graphs, "stock" refers to the default ASUS 5870 V2 clocks of 868/1200, and "overclocked" is the 959/1353 setting used with factory 1.212v and fan on Auto.
Let's see how the card does in 3DMark Vantage.