Don't believe those claims, manufacturers add a large safety margin into their recommendations to allow for cheap & nasty power supplies and a wide range of hardware.
I stand by my good quality 550W+ statement. I linked this site earlier http://www.extreme.outervision.com/PSUEngine
I just put your intended system specs into it and added a couple extras for good measure, allowed for 10% capacitor aging and 100% peak system load. The minimum PSU requirement came out as 521W and the recommendation was 571W. You can be sure they have a safety margin in that calculation as well. If you want to be absolutely safe go for a 650W PSU, gives you a bit of headroom for different hardware choices also.
As a frame of reference when I was lightcoin mining I had 2 x 280X cards running on a single Seasonic 650W PSU at 100% load 24/7 and a cobbled together system with a 7970, 7850, and 6850, all running off a single 750W PSU. To be fair lightcoin mining does not use much CPU so a gaming system could peak a bit higher than those by 100W or so in theory.
Bookmarks