I know this is a pretty meaning less question. I have a pretty modest system that will have a Phenom II 550 (unlocked to quad), 2 HDD, 8gb ram, and a 9600GT. I have a Enhance ENP-5150GH 500W, 600W OCZ ModXStream Pro, and an ENERMAX EIN720AWT. I know any of them would be more than enough for my system but wanted to see if I would be better off using the 500W because power supplies tend to be more efficiant some where in the middle of there range. I'm not sure how fast they drop off at the low and high end of there range some maybe it makes no difference at all. Thanks