GTX 660 TI vs a Radeon 7870 a fair comparison?

Not sure about the second part my guess is they are probably pretty close. I do believe you have a fair comparison there.

I'd say the 660 is more comparable to the 7870. The 660 ti is about 10-15% faster than the 7870.

GTX 660 Ti vs HD 7870: http://www.anandtech.com/bench/Product/548?vs=647

The 660Ti is better compared to a 7950, a card thats ~$50 more expensive than the 7870.
In some aspects the 7870 matches performance, but in general is behind.

the GTX 660 Ti is a solid and relatively consistent 10-15% faster than the 7870, while the 7950 is anywhere between a bit faster to a bit slower depending on what benchmarks you favor. Of course when talking about the 7950 the “anything but equal” maxim still applies here, if not more so than with the GTX 670. The GTX 660 Ti is anywhere 50% ahead of the 7950 and 25% behind it, and everywhere in between."
http://www.anandtech.com/show/6159/the-geforce-gtx-660-... That is a old review though so i am not sure now.

So a 660Ti would be faster than a 7870. Now what if you put it up agains a 7950? Also what is the difference between the GTX 660 and 660TI?

Look here is a example of how 660 ti preforms scroll down page and play the videos http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=w...

The 660 ti vs 7950 http://www.anandtech.com/bench/Product/550?vs=647&

The 660 vs 660 ti http://www.anandtech.com/bench/Product/660?vs=647&

The 7870 is slightly slower than the 660 ti but should be faster than the 660. I would say with the new drivers the 7870 is very much compatible to the 660ti in most games in terms of performance but the 660ti should still be somewhat faster.

This depends on the settings you play one as well as the resolution, things like MSAA really brings down the 660 ti.
http://www.hardocp.com/article/2012/11/12/fall_2012_gpu...