This amounts to the unstoppable force going heads-up with the unstoppable force, and based on the improved skills of both men, especially GSP, this promises to be a great fight.
That being said, I think GSP will be able to use his superior stand-up and athleticism to keep Hughes off-balance away from his own strengths. Watch the leg kicks, I think they are going to be huge in this fight. Leg kicks could take either man out of his game, reducing the effectiveness of the shoot.
This should go 5 rounds in my opinion, but I think this really going to come down to the old cliche of who wants it more, and no one is hungrier than Georges St. Pierre. GSP by rear naked choke.