Card was tested with i7-2600K @ 3.4GHz and was compared to GTX 680.
3DMark 11 Extreme Preset:
GeForce GTX 660 Ti (915/980/1502 MHz) – X2730
GeForce GTX 660 Ti (1015/1080/1502 MHz) – X2880
GeForce GTX 680 (1111/1176/1502 MHz) – X3621
3DMark 11 Performance Preset:
GeForce GTX 660 Ti (915/980/1502 MHz) – P8321
GeForce GTX 660 Ti (1015/1080/1502 MHz) – P8792
It’s almost certain that the final clocks are 915/980/6008 MHz (base, boost, effective memory).
Since this is still a GK104 it has great overclocking potential.
So without greater difficulties card can reach 1.2 GHz core clock, and at that point card is performing almost as fast as GTX 670, not to say it has the same performance.