You should check out my thread comparing performance in BF3 benchmarks...
The 570 has a higher performance ceiling, and gains much more from overclocking when compared to the 6970...It's also been noted that the AMD cards are struggling badly in BF3 with MSAA enabled. It's a toss up honestly, but if you plan on maxing BF3 I would go with a non-reference 570 and sli later on.....Check out this little tibit from Techspot.com...
While some things have changed since we tested the Battlefield 3 beta a month ago, overall the performance trends were very much the same.
Being blatant for a second, the Radeon performance both sucked and impressed. Both AMD and Nvidia supplied us with their own version of a "reviewers guide" for Battlefield 3 along with their latest drivers.
Nvidia didn’t bother to compare their products to AMD’s when putting together their reviewers guide. AMD, on the other hand, included extensive testing putting products from both companies head to head. That testing cast the Radeon series in a good light, however we found it odd that in virtually every test AMD used the Ultra settings but with MSAA completely disabled.
When we started testing on our own it became apparent why AMD did this. With MSAA enabled the performance sharply declines with Radeon boards and previous generation Nvidia products make AMD’s current generation hardware look foolish.
However disabling MSAA allows AMD to catch up to Nvidia, as you saw in our High quality 1680x1050, 1920x1200 and 2560x1600 tests.Edited by RawFoodPhil - 10/29/11 at 9:33am