The gtx 690 is stronger than a gtx 780ti. The 760 is mid range, 690 high end. Unless you are cpu bottlenecked, the fps difference will be huge.
Expected fps are hard to call, depending on settings, resolution, amount of monitors, game and cpu. But you can expect the 690 to give you >60 fps on any game on ultra in 1080p. The 760 would possibly do around 30 fps then.