Power supply is overkill for what you are building. I have an antec 750 watt psu and its already more than enough to power 3 overclocked 5830's, which each use way more power than a GTS 450. Stock i7 : ~= 95 watts, stock GTS 450 ~=106 watts Average rest of system ~=75 watts. I would say a good, sub 500 watt psu would be plenty for this build.