By itself it won't draw more than 350W I think, leaving 250 for the rest. I don't know what an OCed i7 would use but the TDP is 125W if I'm not mistaken. I doubt it'll double the maximum usage. RAM doesn't use too much, leaving harddrives, motherboard and add in card. 600W may be the real usage, but you need to keep in mind the efficiency overhead of course.