The GPU is fine, I wouldn't swap it for a 570 as that 6950 can unlock to a 6970 (there's a thread on it somewhere). In terms of buying a PC to run a game that's not even out yet, I'd wait and see how it runs on certain hardware if I were you. Second-guessing system requirements is always a risky business.
(That's not to say it wouldn't run on that system, I'd guarantee that it'll run just fine, but it depends on how picky you are. If you desperately want to run BF3 with all the eye candy on then I'd wait).