I have been having problems on my new 920 machine, with it locking up. First I thought too much OC, went all the way down to 3.4, and it still locked up. Then I thought PSU, so I changed out the 1010 watt unit with a Corsair 750. No change. Then another guy on the CPU forums was having the same problem, in an I5 750 and an ATI 5770, and he updated his video drivers, and that fixed it. So I updated to 195.(something) nvidia drivers and I got 500 ppd on the same units !
When I get time I may upgrade the rest in the house.
As for power, I have my machine spread over 4 breaks, one is a 20 amp circuit.
EDIT: The second box I put it on, made it EUE on both GPU's !!!! I am reverting back to 182.06 on that box.