GK104 is a very powerful GPU, but it seems to be bandwidth limited at resolutions over 1080p.

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Res....... 7970 ...... GTX 680 .....
1050p: 133 fps | 162 fps (122%)
1200p: 118 fps | 135 fps (114%)
1600p: 082 fps | 083 fps (101%)

Now imagine that GK110 comes with 384 bit, or even 512 bit bus width. Even with 'just' 50% more shaders it should be able to pull 60%+ ahead.