Dave178. I have a 520W PSU and it runs: 2500k, 660Ti, 2HDDs, 1SSD, 3 case fans, and a DVD drive. I'm not sure why you would want 650W unless you were considering SLI/Crossfire in the future.
btw. The 660 is a great deal. (not overpriced like my 660ti was) It'll rock BF3 on High at 45+fps at least.