Overclocking
We've used the same overclocking philosophy on this card as on previous Radeon HD 7970s. This entails keeping the core voltage at 1.17V and increasing clocks until the card can no longer run four loops of Crysis 2 at 2,560x1,600.
And there you go. The reported numbers are at the very high end of what we've achieved with partner-overclocked HD 7970 (non-GHz) models, suggesting that the yields have indeed improved over time. We therefore expect to see overclocking-focussed models to come in with a core speed in excess of 1,200MHz.
A bit of jiggery-pokery and voila, the HD 7970 GHz Edition sneaks ahead of the GPU-Boosting GTX 680 - at 2,560x1,600, at least.