I don't think anyone in their right mind would have predicted the 7970 would outperform the 6970 by 80%+ unless we had some concrete info.
HD7970 is nowhere near 80% faster than HD6970. It's roughly 42-45% depending on the source. To be 80% faster it needs a 30% overclock. And actually, in the past almost all major AMD generations were accompanied by 60-100% performance increases (once you include modern games at that time),
at stock speeds. No overclocking required. The same for NVidia.
You can use
Voodoo Power Ratings that nicely summarizes the performance increases. This is very accurate despite looking like an amateur's work. You can look up launch dates using GPUreview.com.
Based on historical cadence of NV, Kepler's high-end should be about 60-70% faster than GTX480 and 40-50% faster than GTX580. We don't know if that happens, but it is easily in-line with the past of NV's own GPU generational leaps.
GPU evolution (last couple generations).
GTX580 > GTX280 by 73% (which means about 60% faster than GTX285)
GTX480 > GTX280 by 51%
GTX280 > 8800GTX by 63%
If you take more modern games, the difference is even more.
There's been a 20-40% increase with each generation? GCN didn't jump by 20, but with some light and easy OCing the 7970 performs as well as a crossfired 6970 setup. That's not predictable, that's insane.
Actually that's not true. AMD has never increased performance from 1 major generation to the next by only 20-40% aside from HD5800--> HD6900 (but
6000 series shouldn't have been labeled as a 6 in the first place).
Your very own HD5870 spanked HD4870, often by 2x, at
stock.
Here is
a review.
From that review, I quote:
"When compared to the Radeon HD 4870 the results are staggering, as we saw an 83% performance gain on average, with the Radeon HD 5870 delivering more than twice the average frame rate at 2560x1600 in games such as Far Cry 2, Company of Heroes and Wolfenstein. Just 2 of the games tested dipped below a 60% performance gain, and those games were World in Conflict and Supreme Commander.
Commonly the Radeon HD 5870 appeared to be between 65% and 85% faster than the Radeon HD 4870, which was truly impressive."
That's at stock speeds.
Here is
another review:
"...the single-GPU Radeon HD 5870 actually managed to outperform the Radeon HD 4870 X2 in 6 out of the 15 games tested...The Radeon HD 5870 also beat the GeForce GTX 295 in 5 of the games tested"
In how many games does an HD7970 outperform HD6990 or GTX590? It needs a 30% overclock just to match them.
Finally, before that:
8500 --> 9700Pro = > 100%
9800XT --> X800XT = 75-100% increase
X800XT --> X1800XT = 75-100%
X1800XT --> HD2900XT/3870 = 75-100% (* this one is tricky since if you count X1900XT as a half-generation then it alone brought 30-40% in shader intensive games over the X1800XT, but that diminishes the gain of the HD2900XT to follow)
HD3870 --> HD4870 = 50-75% (at least)
HD4870 --> HD5870 = at least 60-80% faster on average and more or less 2x faster in modern games.
In fairness to HD7970, with overclocking, it does get to 70-100% faster performance over HD5870/6970 in the most demanding games today (Crysis 2, BF3, etc.)