If BF3 Multi-player is your goal, you will need a quad core for seamless play. a i3 2120 plays well on most multi-player 64 maps, but can be occasionally laggy on some. this is according to my son playing on our HTTP i3 2120/HD 6850 on high settings vs playing on his i7 2600K/GTX 570 system. he's says its still playable but he does notice. single play he sees no difference.
Slightly over $500 but a solid system for BF3. It even has SATA 6G and USB 3.0.