Performance Summary Diagrams
The first two pairs of summary diagrams should help you estimate the advantage of AMD Radeon HD 6970 2 GB over HD 6950 2 GB in nominal operational mode and during overclocking of the latter to 870/5880 MHz frequencies. The zero axis is the performance of Radeon HD 6950 and the performance of the flagship HD 6970 product is shown in percents from the latter:
Radeon HD 6970 is on average about 10-11% faster than Radeon HD 6950 without antialiasing and about 11-13% faster with enabled AA. It is remarkable that this graphics card reaches its highest (20%) and lowest (2%) performance advantage in the same game: StarCraft 2: Wings of Liberty. The reason for that is fairly simple: AMD Radeon graphics cards behave inadequately when antialiasing is enabled. Overclocking helps Radeon HD 6950 almost eliminate the performance difference from HD 6970, and in some games and test modes even outperform the latter.
The next set of summary diagrams compares nominal Radeon HD 6970 and HD 6950 against GeForce GTX 570. The results of the latter serve as a zero axis, with the gain or lag of the new competitors shown as percentage from this axis:
This battle ends with variable success on both ends. Since there is very small performance difference between Radeon HD 6970 and HD 6950, GeForce GTX 570 manages to successfully compete against both of them. We see parity between AMD and Nvidia or a tiny advantage of either one of them in quite a few games. In some games like Tom Clancy's H.A.W.X.2, Lost Planet 2, Borderlands and high image quality modes in StarCraft 2: Wings of Liberty GeForce GTX 570 is an obvious winner. In other games, Radeon HD 69xx is faster. It is hard to draw a definite conclusion here, because besides the gaming engine we should also keep in mind image quality settings and screen resolutions.
Finally, the third pair of diagrams is dedicated to comparing Radeon HD 6970 against Radeon HD 6870, both being top graphics accelerators in their class. The performance advantage of the single-processor AMD solution is shown in percents from the performance of HD 6870:
Looks like Radeon HD 6970 outperforms Radeon HD 6870 on average by 26-31% without antialiasing, and by 27-45% with antialiasing. The very last diagram shows the benefits of having 2 GB of video memory onboard: in some games the performance difference between the two cards is truly impressive.