I'd like to point out that most HD 7850s available on the market comes overclocked to 975-1000 out-of-the-box and the reviews you see are of 860MHz (+/-), so please avoid them. HD 7850s are on par with GTX 660s from NVIDIA and are very much overclockable on stock voltages as well.
Here's an example:
Gainward GeForce GTX 580 Phantom 3GB at stock (thanks to OCN member DarkSamus for posting his/her result) - http://www.3dmark.com/3dm11/6527446
Graphics Score: 6408
Graphics Test 1: 28.1 FPS
Graphics Test 2: 29.5 FPS
Graphics Test 3: 42.1 FPS
Graphics Test 4: 20.6 FPS
HIS Radeon HD 7850 IceQ X Turbo 2GB at stock (my GPU results) - http://www.3dmark.com/3dm11/6524127
Graphics Score: 6623
Graphics Test 1: 27.6 FPS
Graphics Test 2: 31.6 FPS
Graphics Test 3: 43.6 FPS
Graphics Test 4: 20.8 FPS
Now, why I'm posting GTX 580 scores? Because GTX 660 is NOT significantly faster than the GTX 580 (if at all) so you can expect GTX 650 Ti Boost to be slower than the GTX 580 too, thus slower than the HD 7850 as well.Src
Now some might argue why would you compare a "factory overclocked" to a "stock" GTX 650 Ti Boost? because it's all about "clocks" which already have been increased in the "Boost" edition of the GTX 650 Ti (also includes improved bus interface) but even a "Superclocked" variant of the card lags behind the GTX 660 (see below picture from TPU). Src
I know 3DMark 11 is a "synthetic" benchmark but still it gives most unbiased results thus far.
Good luck OP.