About to upgrade my GPU to a 5870. Seeing as how I have my CPU constantly OC'd, sucking up a lot more watts (saw one link showing a OC'd CPU can suck 150+watts more than normal), I'm thinking I'm going to have to upgrade my 600w PSU.
No. More like 20 - 25% more.
Example: based on actual measurements with lab calibrated military test equipment, the current drain of my Q6600, OC'd to 3.6 GHz, went from 8 amps to 9.5 amps. Power consumption increased a little less than 20 watts.