Upgrading from a 5970 to 6970 crossfire was already a mistake....
I'm using 3x30" screens at 7996x1600 so I really needed the 2Gb VRAM. Some demanding games sure run a lot more smoothly now, and I can use higher settings including AA. But I agree that it is not an improvement in every way. I thought that the 5970 is simply crossfire on a single card, but now that I have "real" crossfire I find it comes with a few more issues. I hope this is at least partly because the drivers are still young.
The 6990 could be an interesting card, but figured it may not reach 2x6970 performance due to power/thermal constraints.