Really, when you look at the performance the HD 6990 4GB offers out of the box there's not really any reason to flick that BIOS switch over to position 1 and unleash the beast that is AUSUM mode. So you find yourself wondering, why flick the switch, throw more voltage through the card and push the clocks even further?
Well, I answer that question with another question! Why not? Sure, you probably don't find yourself overclocking for everyday use, because it's not really necessary, especially at the moment as the card eats up every game benchmark at any single screen resolution. If you're going to benchmark, though, the chances are you're going to want to overclock and if you're happy to get right into benchmarking, you can push that core to 1GHz while pushing the fan to 100%.
More often we overclock because we want to, not because we need to. If you want to make use of even more power and don't mind the extra dBs that the setup will carry, go for it, but if you buy yourself a HIS HD 6990 4GB and don't touch overclocking or the AUSUM switch and you're going to be just as happy.
The HIS HD 6990 4GB is a great card and it feels like it's been forever since we saw a dual GPU model not just from AMD, but from anyone. It's here now and while stock is a little in and out, you shouldn't have too much trouble getting a card. The biggest problem at the moment might be getting one for $699, as there seems to be a little bit of an early adopter's tax thrown on top. Still, at an extra $20 or $30 the card continues to be amazing and at $699 the extra few dollars don't seem as significant.
HIS has done a fantastic job with the package by including a load of convertors that are going to make getting the card up and running straight away with any monitor an absolute breeze.
As you would expect, the HIS HD 6990 4GB is a fast card and overall just a great card for people who demand power. Overclocking potential clearly exists, but it's fairly safe to assume a lot of people probably won't bother due to the simple fact it's not really necessary.