Maidana would constantly get to Gatti and stop him in the mid rounds. Maybe Gatti lands a miracle left hook, perhaps a body shot like the one that Khan dropped Chino with, but more than likely I think Maidana stops Gatti. Gatti would try to box and get caught with Maidana's wild caveman punches. Whether or not he continues to try to box and use the ring, or gets drawn into a war, he'll still keep getting hit with hard shots that will wear him down.
Maidana in a war. I don't think either guy is elite, but Maidana's edge in power is key here. Gatti is just not disciplined enough to fight from the outside and stay out of exchanges. I think both hit the floor, but Maidana will recover to finish Gatti in 8 rounds.