Yes, $260 for a 660 Ti is a really good deal. It is used to be $300 so you have a $40 sale. The 7870 should be slower (but in a really small margin), or if not trade blows with the 660 Ti, considering that the 7870 is now $250, I think 660 Ti is still a better choice at $260.
The 7950 (without Boost Bios) will be a bit faster than the 660 Ti, but it will cost $320 normally. If you are comparing with the 7950 with Boost Bios, it will blow away the 660 Ti .