I went to
eXtreme Power Supply Calculator Lite v2.5 and took the specs in your sig assuming you have 2 SATA hard drives and 1 optical drive & 3 random USB devices that pull power. It says you need 380w even with your q6600 oc'ed to 3ghz. With the video card upgraded to the power hungry GTX 280 it says 426w, in SLI 576w. 2 4870's in Crossfire was 515w and the 4870x2 wasn't listed.
A lot of people fall into the marketing hype of bigger is better - especially when it comes to power supplies. My advise to anyone - Choose a quality one for your needs with some breathing room. Everything is listed at max. load and you would have to be stressing ALL your components to the max to ever hit that. Video cards are listed with high requirements so they can cover their asses. Your enermax will do you for a while in my opinion.