Hawken which is still beta but uses physx, im getting pretty steady 45-60 dependent on map with full everything 1080p and full physx. Metro LL full settings, not sure the FPS but i never get a skip or jitters, always smooth. Warframe, also in beta but pretty good graphics. Full settings, not sure what my fps is but again never any skipping. Other games that are less demanding or intense run without issue of course like LoL, Batman AC, etc.
Id imagine a 760 would run even better and i think they go for about $250 now, a 770 would be sweat but i think that goes for around 400-500. 2x 760's id imagine would be > 1x 770, but im not sure. Also not sure if sli is an option for you.