650 will work.... but if you are planning on xfire at some point in the future, 750W min. better to spend the extra $20 or so now, then have to buy a new video card and PSU in the future. just a suggestion.
Also, get a quality PSU... i like Corsair. its the heart of the system. if it goes, it can take out all the other components as well...
That will run circles around the AMD Phenom II 960T any day of the week. It may run a little more than what you have already but it shouldn't much.
I will also definitely reiterate what was said about the PSU - do not skimp or compromise on it, the wrong one can quite literally blow up in your face - I've had that happen on a couple of occasions and I'm really picky about the PSUs I've chosen as a result.