Hashing stress and gaming stress are very different things.  Case in point, everybody can downclock their Graphics card memory to a ridiculous degree, and this works wonderfully for mining, but try that while trying to fire up Crysis and watch things grind to a screeching halt.  Test your cards, one by one, in a live fire exercise - mining under stress.

Also... Raidmax PSUs are really that bad.  Never trust their box numbers.  They can handle normal usage just fine, generally, but the constant and steady drain taxes them in dangerous ways.  If you're using raidmax PSU's, it really is a possibility that they are the problem!