What is the monitor resolution?
With this class of card resolution is very important, especially if you use AA, the 7770 has a narrow 128 bit memory interface and suffers a heavy framerate loss with AA applied, if you're having issues try turning AA down or off.
The GTX650 Boost has a wider memory bus and higher frequencies than stock 650Tis' making it faster overall and less likely to suffer heavy framerate penalties with AA enabled:
http://www.tomshardware.co.uk/gaming-graphics-card-review,review-32671-7.html
Depending on the games you play and resolution, you might want to push it up another tier and look towards the GTX660/HD7870 class instead.