Overclocking & Thermals
The cooling solution ASUS has designed for the Extreme N7800GTX Top just screams at you to overclock it. The HSF on the card is significantly larger than the stock reference design and again, the design vents heat outside of a case through the card's back-plate. We first performed some extensive testing in thermal characteristics of the card and then pushed the clock speed sliders as far as they could go before becoming unstable.
|In an effort to understand just what the ASUS Extreme N7800GTX Top's cooling solution affords you in terms of thermal performance, we took our entire test system and dropped it into a well-ventilated chassis with a 520 watt power supply. We then took readings from all available temperature sensors in the system at full load while running our current favorite graphics stress test, Masaki Kawase's DX9 "Real-Time High-Dynamic Range Image-Based Lighting" benchmark, or "rthdribl" for short. This test easily will take a GeForce 7800GTX card up to its flat-out top end temperature with demo loops that seem to work nearly every transistor on the GPU driving High Dynamic Range rendering effects.|
There are obvious advantages to ASUS' "OTES" (outside thermal exhaust system) style cooler from Artic Cooling that is mounted upon the Extreme N7800GTX Top. First, you should notice an overall drop in system temperature whether running a single card or in an SLI config. In fact we achieved a 4oC improvement over the stock GeForce 7800GTX cooler used on the BFG card we tested. Even more impressive perhaps is that the system temperature did not change when we dropped a second card in for our SLI testing.
Host CPU temperatures in our test system remained the same within any of our test configurations most likely because this test is hugely dependant on GPU throughput. Which brings us to the final and most impressive data points in our graph. A single ASUS Extreme N7800GTX Top ran on average a whopping 15oC cooler than our slightly overclocked BFG GeForce 7800GTX OC card, which again is running a 26MHz slower core speed of 460MHz versus the ASUS Extreme N7800GTX Top's 486MHz core GPU speed. In an SLI configuration with two ASUS Extreme N7800GTX Top cards installed, the primary GPU (closest to the CPU socket) temp went up another 5oC to 68oC but the second GPU leveled off at 62oC. In short, not only does the ASUS Extreme N7800GTX OC run significantly cooler in a single-card configuration, but an SLI setup will also run cooler than virtually any single stock reference GeForce 7800GTX cooled card. Further, overall system temps most likely won't change much either if/when you drop that second card in an available slot. We will of course caution you that your experience with a different case, power supply, or other components may be measurably different than what we've shown you here, but you knew that...
Overclocking the ASUS Extreme N7800GTX Top can be achieved through a couple of methods, whether via ASUS' own "Smart Doctor" utility (pictured below) or with NVIDIA's Coolbits registry tweak.
In the end we were able to take the ASUS Extreme N7800GTX Top to a peak GPU speed of 505MHz and Memory speed of 1.4GHz. In SLI testing, memory speed was limited somewhat further to 1.36GHz, just 10MHz over the board's stock 1.35GHz speed. Although our testing allowed a core speed increase of about 4%, 3DMark05 showed a much smaller, less than 2%, increase in its final score. Frankly, although the ASUS Extreme N7800GTX Top's overclocking potential is good with the enhanced cooling solution it offers, we're much more interested in its significantly improved thermal performance and ultra quiet operation. And let's not forget the fact that the card essentially is already overclocked pretty heavily out of the box at 486MHz for the GPU and 1.35GHz for its Memory, along with a full three year warranty to back it up.