[quote name='vpyroman2']You'll need a 650W minimum power supply to ensure you don't ruin it when you're playing games with maxed out graphics. Someone feedback-ed they had a 520W but that's really unwise.[/QUOTE]
I have a 430w PSU supplying my computer which includes an i7 870 and Radeon HD 5770, and I max out games just fine. You do not need a huge PSU if you have a well made, efficient one.
That said, I'm wondering if the 6770 is worth it upgrading from the 5770, or if I should just save up some extra money and spring for a better nVidia card. The microstuttering I've seen discussed in regards to AMD cards (and that I experience in a number of games) is almost enough to make me jump ship from one brand to another.