Overclocking is a bit of a funny thing and depending on the way companies set up the fan profiles can depend on the kind of overclock you're able to achieve. We can see for ASUS, silence continues to be something they want to concentrate on and even when we add more voltage to the card, the fans don't ramp up to these unbearably loud numbers.
The problem with that setup, and we see it a lot with Palit cards, is that the overclock just isn't going to be as strong versus a company that tells its fan or fans to ramp up to 80%+ when the cores start to really heat up. The thing is, though, you find that the MARS II creates a much more bearable card in gaming because it doesn't shoot up to 80dB.
Instead, you can give yourself a nice overclock that yields a good performance boost, and you get a setup that is outputting the same noise levels as a stock GTX 580 in SLI setup. Not only that, though, we've got a card running cooler than that stock GTX 580 SLI setup and that's where so much of the appeal to this card is when you step outside of the performance side of things.
It's worth mentioning, though, that if you want to get into the benchmarking side of things you can always hit the little 100% fan button and crank up those two fans to full speed. That will help bring with it lower temperatures which will in turn give you a larger overclock. The good news is that even at 100% the fans aren't that bad thanks to the fact that ASUS have opted to use 120mm fans.
At 100% fan speed the MARS II is less irritating on the ears than the HD 6990 in its AUTO profile thanks to the size of them. If you wanted to, you could crank the fans up to 100% every time you gamed if you wanted the biggest overclock, but I'm not sure why you'd bother. Everything we throw at the card today runs like a dream and the need for even more speed is probably quite unnecessary. Of course, that doesn't mean you can't do it.
Overclocking the MARS II just simply brings us more performance than what we've already got, which to be honest is more than you'll probably need. Of course, that all doesn't change the fact that we just love to see how much more performance we can get out of the card and the fact that we're over 850MHz on both cores and getting noise levels in line with the reference GTX 580 setup in SLI is amazing.