B.J. Penn was never really beat up at 155lbs, but there were a few times when he clearly became frustrated fighting in the welterweight division. Georges St. Pierre and Matt Hughes have each been able to give Penn trouble over the years, and if anyone can replicate that kind of top-game control it's Jon Fitch.
Hughes forced Penn to fight off his back at UFC 63, eventually taking the fight by technical knockout after Penn suffered a rub injury. At UFC 94, St. Pierre carried a similar gameplan into the cage and Penn was once again bullied by a much bigger, prominent wrestler. Viewers could clearly see the frustration on Penn's face during both fights, leading many to believe that the former champ could be forced to mentally check out if put under enough duress.
I can only assume Jon Fitch is planning to try something similar. He certainly has the style to carry it out. If Fitch can hold someone like Thiago Alves down for three rounds, I don't see why he can't do the same to a much smaller fighter like Penn. BJ's takedown defense is on another level entirely, but I see Fitch using constant pressure in the clinch until he eventually gets the fight down where he wants.
Fitch hasn't dropped a fight since 2008, going 5-0 since his title shot with GSP. He dominates fighters for three rounds, using his superior wrestling to overpower his opponents and drag fights into decisions.That's exactly how I see this fight going.