786? Don't you mean 768?Anyway... 768Kbps translates to 768/8=96.
If you're able to reach ~96kB/s or somewhere below that, then you're certainly making full use of your connection.
How well you will be able to play depends on how much bandwidth a regular game of Smash will actually need, where the players you're playing with are located, and how stable your internet connection is.