You could probably run it on a 320-watter with no problem. You're amps are fine.
look at this:http://forums.slizone.com/index.php?showtopic=405
This guy SLI'ed 2 8800GTS's and is not even getting above 400-watts @ stock. I'm not worried to use an e8400 with SLI'ed 8800GTS either.
People seem to buy way more power then they need. Any gamer that has a budget below $1500 will not need more then 600-watts of power, unless you have like 12 cheap hard drives or a really sucky 600 watt. (correct me if I'm wrong).
Check out Jonnyguru.com. There is a wealth of PSU information on there, as the guy who made the site works for BFG Tech's power supply division.