Well it seems the GTL's are doing something positive, I would try next 0.70x GTL REF's and 1.44v vFSB if the current setting fails. Maybe also bump up vcore 1 more notch too. It's just pure trial and error. Good luck with it, it's late here and I have to go get some sleep. I'll check on your progress tomorrow, and perhaps someone more knowledgeable with quads can offer some advice in the meantime; I'm good with duals but have never owned a quad.