A couple of comments.
Thermaltake, Corsair, OCZ; all, generally good stuff...check reviews.
Memtest86: http://www.memtest.org// Will help rule out failing memory.
Back to PSU's.
Single 12 volt rails are nice, but in the very high power range, they are problematical.
With multiple 12 volt rails, you, obviously, have to ensure that the load is properly balanced.
One other thing; you stated an issue with the 5 volt line. Using lots of USB devices?
If so, consider getting an externally powered USB port (Belkin makes a nice one). The 5 volt line is very often overlooked, and very often the source of otherwise inexplicable shutdowns.
Good luck