Better at what ? At what resolution ?
If it's gaming at 1920 x 1200,teh results are very close but these numbers should help you decide:
Guru3D uses the following games in their test suite: Hard Reset, COD-MW2, Far Cry 2, ANNO 1404, Metro 2033, ANNO 2070, BFBC2, BF3, Crysis 2, AvP, Lost Planet 2.
7950 gets 746 fps at a cost of $0.41 per frame
660 Ti gets 851 fps at a cost of $0.34 per frame
TechPowerup uses Alan Wake, AvP, Batman Arkham City, BF3, BattleForge, COD4, Civilization 5, Crysis. Crysis 2, Dirt 3, Dragon Age II, Hard Reset, Metro 2033, Stalker CoP, Starcraft 2, Shogun 2, Skyrim, WoW, Diablo II, Max Payne 3, Sniper Elite V2 in their test suite. They're totals are:
660 gets 1387.41 fps at a cost of $0.21 per frame
7950 gets 1348.2 fps at a cost of $0.23 per frame
Hardware.Info uses AvP High 4AA, Batman AC Very High 4AA, BF3 Ultra High 4AA, Crysis 2 Ultra High Edge AA, Dirt 3 Ultra 4AA, Hard Reset Ultra 4AA, Metro 2033 Very High, Skyrim High 4AA and Shogun 2 Ultra 4AA in their test suite. They're totals are:
660 Ti gets 566 fps at a cost of $0.51 per frame
7950 gets 557 fps at a cost of $0.55 per frame
At higher resolutions, these numbers are not going to be relevant. And of course different game lineups will produce different results.