snailI would say at stock speeds the 660ti and the 7950 are comparable in performance. From reading other forums, the 7950 does seem to overclock better than the 660ti.
The 7xxx series also has a problem with frame latency which AFAIK, is still being fixed.
Dont quote me on the last part, it might already be fixed :c
http://techreport.com/news/24136/driver-software-to-be-tweaked-to-reduce-radeon-frame-latencies-in-series-of-updates
The 660ti's 192bit memory bus is pretty limiting and not very future-proof. Might be a minor issue with next gen engines coming out soon. Just something to keep in mind.
the ti version is literally no more than 10% better than the stock 660 yet is over 70 dollars more. Just like the difference between the 670 and 680, if you oc the 670 it'll pretty much preform like a 680 and saves you a ton of cash to get whatever else you want like ram or an ssd etc