Can you run three monitors with a single GTX760? Yes. Can you run games at Ultra settings with a single GTX760? No. There are several limitations that are involved. VRAM buffer of 2GB is not enough to play games at the higher resolutions used whenever playing games in surround mode and the GTX760 is not powerful enough to play most modern games at higher resolutions and still maintain a playable frame rate - even with the in-game graphics settings turned down. For example, in order to play Crysis 3 at 5760 x 1080 surround resolution (three 1920 x 1080 monitors) at Ultra settings you would need three 4GB DDR5 GTX770s (or higher model) in order to have enough graphics processing power and VRAM to do so. If you drop the graphics settings to medium, you might be able to play the game using only two GTX 770 cards (or higher model), but would still need the larger VRAM buffer size.
Another consideration is that you may need to also upgrade your power supply in order to run two or three graphics cards in an SLI configuration.
The bottom line is that surround gaming is not an entry level decision and requires the individual gamer to seriously consider spending thousands of dollars to enjoy such a setup.