BJ and GSP is going to be on the best fights you'll ever see
I don't know man, their first fight sort of sucked. if BJ gasses, this could be painful.
Penn still has some decent match-ups at LW: Florian, Griffin, Sherk in a rematch, possibly Gray in a few more fights. It's not like there's nobody. Plus, BJ's the man at LW. I'd rather watch an awesome BJ than a good BJ.
GSP can still fight guys like Alves, Diego, Swick, Karo in a rematch, Yoshida, etc.