I have an 850W PSU. You should get a 550W or larger for those graphics cards and larger than that if you plan to future crossfire/SLI. I'd get an 850W and use it for the next 4 years. Then get your graphics after that. (Buy Corsair, Antec, Seasonic, Silverstone, or XFX).
An SSD won't improve your fps at all--just load times.
As far as graphics, I love the 6950 2GB with unlocked 6950 bios option. For $260, it's an amazing deal. (Although not the 5870 for $179 deal like Newegg had last week).
If you upgrade your graphics to a 650W if I was gonna SLI a second GTX 460 1GB--which is probably the best option (unless you've got a good deal of extra cash). Check this site for power requirements: http://extreme.outervision.com/psucalculatorlite.jsp