I currentlly play crysis 3 on 6770 on meduim with 25 to 30 fps
If you already have the 6770 it's not worth getting the 650, or probably even the ti boost. Save a little more money and do a significant enough upgrade to really make a difference in the game, like the GTX 760 or HD 7870LE.
The GTX 650 is the superior card, but I would get the 650ti Boost for just a few bucks more. Pretty significant performance increase for the small amount of extra money.
For Crysis 3 and BF4, don't expect stellar performance. Crysis 3 is one of the roughest games out there right now, and BF4 will likely be similar. It's not that the GPU is poor quality, it's just that it's a sub-$200 GPU on incredibly rough games.
the gtx650ti will be a tad bit faster.
I recommend you getting the boost edition though... its just a small difference in price for a big boost in performance.
for the AMD equivalent, i recommend the 7790 if you're tight on budget or the 7850 if you have the spare money.
I currentlly play crysis 3 on 6770 on meduim with 25 to 30 fps
If you already have the 6770 it's not worth getting the 650, or probably even the ti boost. Save a little more money and do a significant enough upgrade to really make a difference in the game, like the GTX 760 or HD 7870LE.