Ummm... this is normal. As you increase frequency, you need ever increasing amounts of power [voltage] to keep the chip stable, reducing efficiency.
dude!!! u completely missed the point:) i'm talking about a much more drastic increase in power than normal, its something to do with resonance, and the resonant frequency....anyway forget it!!! cheers
PS:- maybe i shall bring this thread back when Tomshardware 'discovers' an issue with the Vishera chips in September:) lol...just kidding