It depends on things that you haven't detailed. What resolution do you typically game at? How much memory does your 770 have? Do you tend to play lots of graphically intensive games, do you run higher graphics settings (4x - 8x AA, MSAA, SSAO, etc, tesselation, etc.). These are some of the things that factor into whether you should go the SLI route, or, usually more preferable, upgrade to a single higher power, higher memory card, which is the simpler, less headache-prone solution.