This is my answer in an identical thread from yesterday:
Yes, the 6850 is definitely the better choice. See benchmarks here: http://www.anandtech.com/bench/Product/539?vs=541
I note however that the 6850 is going for about $135 post-rebate. For $15 extra post-rebate, you can get a 6870, which is a substantial upgrade, especially for a game like BF3. http://www.newegg.com/Product/Prod
[...] 6814150521 and http://www.newegg.com/Product/Prod
[...] 6814161389 . See benchmarks here: http://www.anandtech.com/bench/Product/539?vs=540
You could also consider the GTX 560, which is about $145 post-rebate for some models. It will have slightly better BF3 performance than the 6870 and significantly better than the 6850, though I still think the 6870 is the better overall card.
So my overall answer: get the 6870.