Yeah, human smoke is the character with the fastest walking speed, but he's not the fastest character overall since walking speed is one of the less important factor when it comes to compare overall speed. That's why I say that Sonya is the fastest character in the game (less startup frames and less recovery). I always thought that Sonya was the most underated character in umk3. Almost everyone knows that Kano and Jax have the best sweep in the game but not everyone knows that Sonya's one is just as good (it's already in the guide), now I'm happy because I proved it (every characters have the same sweep except Sonya, Jax and Kano, who recover 6 frames earlier.
Edit: In Sonya's character guide, it's written : "... her uppercut hits strangely and deceptively, and it has an extra recovery frame, it looks like the made hers stop one frame too early, but I suppose that makes it hit just a tad earlier"
I'm pretty sure that every uppercut in the game hit on the same frame and have the same recovery (except for Kabal and Sheeva who have 4 extra recovery frames). As uppercuts are the only move on which not having frame advantage add on frame of recovery, maybe it was tested while she didn't have the advantage.