I think the question is WHICH 1200W PSU. Since you have a power hungry CoolIT Elite running off your +12V rails, you may be pushing just one rail a bit too far at certain times which is causing a shutdown.
IIRC, John was having serious stability problems with a pair of ATI 4870's on a similar board/proc setup. Can't quite remember which thread or the exact remedy, but I think it involved altering the clock skew and putting the PCI-E clock back to 100. It's possible that so much data going across the PCI-E bus makes FSB stability a little harder to come by.
Although yeah, crashing on Crysis Warhead right now isn't a sign of instability, it's a sign that you've been playing Crysis Warhead for more than 15 minutes.
i7 2600K | ASUS Maximus IV GENE-Z | 580GTX | Corsair DDR3-2133