eva, thanks so much for this thread! My i7 920 and DFI board (with the latest beta BIOS) have been screaming since I followed some of the stuff in here. I have the 6GB Kingston DDR3 2000MHz kit and it runs perfectly at 2008MHz 8-8-8-20-1T. Just needed to bump the VTT volts up a bit!
So I am running at 4GHz with 1.36v, RAM at 2008MHz with 1.64v, and to keep the QPI stable at that speed, I set that to 1.52v. That's the lowest stable I could get on the VTT voltage.
Again, many thanks!