It says that GTX460 1GB SLI on load eats up 390W and on Furmark 483W.
The stress that Furmark puts your GPU in would rarely be achieved in the real world. So i would 410W-430W would be your load consumption on load (lets say 2 hours of gaming). Add to 150W-200W for the rest of the parts, that depends on what other parts you have. That comes to something around 600W. That leaves you with very little room. Although Corsair and other good brands can deliver stable power at those high loads. But why stress out your PSU just to save a few $$.
That's why get a TX750W.