Firstly, we know very little about FarCry 3.
http://www.pcgamer.com/2011/06/06/farcry-3-preview/
But I'd say you're rig would be fine to play BF3 since I heard of the recommended ( maybe outdated by now though ) requirements from a blog. It said you'd need a HD 6850. So, it should run fine for you since you've got a GTX 570.