Yeah it's gotta be the User, what would any of us know about Video Cards ...
EDIT: For the Record the closer I get to 850 with the 1 Card the slower it run's, 800 seems to be about the max time reduction for it & anything over that just adds time to the Wu's. Not over heating that I can see & have tried up to 1.75 Volts with the card but only running 1.25 right now @ 850 & the card is 4-5 mins slower than the other Card running @ 850 & 1.0 Volts ... Both Box's have the same Motherboard, CPU & the same amount & Type of Memory, PSU's are the same too ...