This was a really interesting piece to do as the setup holds more value to a lot of people because there's already a lot of HD 6970s on out there in people's machines. It paints an extremely positive picture for CrossFireX scaling and overall just creates amazing performance.
Achieving the same memory clock as the HD 6970 should be fairly easy and because you're upping the memory and not the core you don't actually need to increase the voltage on the card, which means heat won't be as bad. To be honest, you could almost try running the HD 6990 in its out of the box mode with the core at 830 MHz and lower stock voltage and try to achieve 880MHz without the need for the extra voltage.
What's funny is that doing this after the HD 6990 CFX setup, this one almost seems to have exceptional value; and it does compared to that considering the price difference is 20%, while the performance difference isn't even 10%. Sure, on a whole there's better value setups, but the TPR paints the perfect picture and that tells us that there's only one setup that we've tested in house faster than this one.
You hate to throw the word value around when you're talking about a video card setup that dives into the four figure region, but if you're already the owner of a HD 6970 2GB the setup becomes a little easier to swallow.
What this setup does over other triple GPU setups from both AMD and NVIDIA is continue to offer you some breathing space on your motherboard. To get this much performance and still have room for a sound card or RAID card is just amazing, and I think that's what's going to really appeal to people in the long run.
Sure, the setup is nothing more than a pipedream for some people, but the performance overall is just amazing and if you've got the money to spend this is exactly the kind of setup you should be looking at. A quick tinker with the HD 6990s memory clock and you're going to have some insane performance in no time. Even leaving the card at stock, though, will yield performance very similar.
I'm a little in awe of the amount of power on offer from this two card, three GPU setup. Simply Amazing!