Total is only $270. If you want to go with AMD, I would step up to a 7870. It will be a bit more expensive, but still in the $300 budget.
I agree with Daedalus's comment about the 660. It's much better for BF3.
However, I would say go with a good 7870. The 660 is good for BF3 but that's really where the big advantages end. AMD dropped the price for its 7870s down, so you can find one for around 10 bucks more than the 660. There is a REALLY big difference in performance between the 7850 and 7870.
I think a 550w would definitely be enough for a 660.
I wouldn't bother with a Corsair CX series model. In my experience, they're not as good as their TX series and other high-end series whereas cheaper XFX, Seasonic, and Antec models are often more comparable to the high end models offered by the same companies than Corsair's CX series compared to Corsair's higher end models.
That's not to say that they're bad, far from it, just not nearly top-notch.