umm yeah.. seems like the game's not really that much heavily threaded as people were expecting it to be..
Still, when a Phenom II X4 (even in O/C'ed) can match the performance of an i5 2500K at much lower price and the OP's primary intention is to play BF3, then thats not a bad buy at all.
Don't go for 6770 CrossFire. Sell and a get a better single GPU.
^Yes, if you can afford to do that, 'coz as I've already discussed, it's fairly GPU intensive apparently and so especially on 1080p, it's gonna be annoying not being able to max things out inspite of having the budget.
The 6770 is plenty good, but only at lower resolutions, or for casual gamers on a budget.