Caporegime
I did have a case of PEBKAC not too long ago when I installed my MSI 7950 over my GB I couldn't get even 1100 stable anymore... turns out my MSI AB installation needed cleaning out completely and re-installing as the cards weren't taking the voltage .
Even the best you see. But because I'm so intelligent I worked it out. It was a secret until now but now you know.
I suspect something like that somewhere is causing a problem for you now because a new driver just doesn't knock 150mhz off of your last stable overclock. That's just not cricket Rusty.