^^^ I agree, i usually wouldn't agree considering the overal cost of the switch, but....if you sell your current rig, you should pretty much cover the cost of switching, and you're likely to get extra performance (with the likes of a 78/7900gt) and an upgrade path, all the more worthwhile.
As for the actual question, 430W should be fine. You could also look at the 450W fortron or the 450W CM real power if the price isn't too much more.