i still think its temps..

try some more prime without fans or something and see if it happens again at a specific temp each time. i have pushed more volts as have other people but depending on the fans & loop, temps will be different. i have push-pull with insane amount of cfm's + very high fpi rads so it keeps temps in check.

edit: do you have some nuts to go on the end of those bolts for your water block?