I vote for the 7950 because it's overall faster, have wider memory bus (not much hit after applying AA), more VRAM and overclocks like a beast(able to perform similar to a 680) and all that for a $20 premium only.
However, if you play games where Nvidia usually have the better performance lead (BF3, etc), a 660ti might not be a bad choice
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.
^^ Except guru3d doesn't keep their drivers up to date so those numbers are not very meaningful, and the problem with the 660ti is minimum framerate, not average, which your post conveniently ignores.
The drivers are the drivers when the card is tested. And I know it doesn't fit preconceived notions but both nVidia and AMD update their drivers....It's not like they update nVidia's and don't update AMD's. If a manufacturer is going to claim foul after releasing a card w/ poor drivers, maybe they should wait a bit before sending the cards out to reviewers.
Performance Boost – Increases performance for GeForce 400/500/600 Series GPUs in several PC games vs. GeForce 301.42 WHQL-certified drivers. Results will vary depending on your GPU and system configuration:
GeForce GTX 680:
Up to 18% in Batman: Arkham City
Up to 15% in Dragon Age II
Up to 10% in S.T.A.L.K.E.R.: Call of Pripyat
Up to 60% in Total War: Shogun 2 (fixes performance issue with latest game patch)
GeForce GTX 560:
Up to 14% in Batman: Arkham City
Up to 5% in Battlefield 3 with SLI
Up to 4% in Dragon Age II
Up to 8% in The Witcher 2: Assassins of Kings with SLI
Up to 7% in Lost Planet 2
Finally, there are three different test suites used.....from three different web sites
The numbers are the numbers. The 660 Ti simply does marginally better at 1920 x 1200 and its cheaper, the 7950 does better at 2560 x 1600.
Here's the sales numbers as % of DX11 cards hitting steam servers in the month of September. Make of them what you will but in one month the 660 has passed the 7950 in sales.....at least among those playing Steam games.
Based on benchmarks I've seen on previous AC release (I think it was AC Revelations), AC runs better on AMD cards. It's quite significant really, although probably can't say the same about AC3. If you'd like I can find some benchmarks links for you but it's definitely better if you find it yourself.