"The Boost technology – in order to function effectively – needs to process data every few milliseconds and adjust core voltage and clock instantly to reduce any “lag” between clock changes and greater demand from the user. If they only updated clocks every few seconds, the experience would be rather clunky to say the least. As you can probably guess, changing core voltage and clock every few milliseconds while trying to benchmark at a 40% overclock isn’t really helping anyone. For that reason alone, this card is sure to fail at extreme level overclocking, and arguably for some amateur overclockers.
For our sample, 1215MHz seemed to be all that we were able to boost to with any sort of reliability issues. This equates to a 159MHz overclock, past the default 1056MHz ceiling, and to be honest it isn’t really worth the hassle. Power draw goes up roughly 25 per cent to 45W, while performance only rose 1-10% over a range of applications. This removes most of the power advantage the GTX 680 has over the HD7970, and performs far worse than the latter when both are overclocked."
"Overall, it’s pretty easy to see that AMD’s Radeon HD 7970 has more to gain from an aggressive overclock than Nvidia’s GeForce GTX 680."
"The other conclusion to fairly easily draw is that Nvidia’s GeForce GTX 680 sees much of its headroom exposed by GPU Boost already, leaving less on the table for overclocking."
For me..my next upgrade has to be a GTX680..unless ATI drops its price down before the end of the week..it makes no sense to get a 7970