ok well my situation is i currently have a 1 gig 6950. i was interested in going crossfire to maximize potential for bf3 and future games. but im also thinking of just buying a 2 gig card because im starting to get the impression that the 2 gig would be better than going 2 1 gig crossfire. i read on a thread somewhere that 2 1 gigs still equal 1 gig in the end.(i'm also playing at 1080p resolution) basically im confused on how is a certain card better than the other if you also have to count the whole vram situation?? for instince would a 2 gig 7870 be better than a 1 gig crossfire 7970
If you have a 1gb card and add a 2gb. The Larger card will scale down to the smaller card. Inn your case Battlefield 3 requires 1.5gb of vram to run ultra. So crosssfiring isn't really gonna help you out here. I would sell your 6950 and look for a better card.
Any of these cards are good options. HD 7850(starts at $230),HD 7870(starts at $290),HD 7950(starts at $340). All of them are excellent cards and have lots of vram.
Best of luck choosing a new card!