Paul Williams has the best chance of beating PBF his size with his southpaw stance and his power being the main factors. Guys like Pac and shane can be outboxed, lesser fighters have done it to them. Cotto can be hurt easily is one-handed and doesn't fight smart he won't beat PBF. As for Margo no comment.
No. I would give Pac nearly no chance. At 147, Floyd (assuming no degradation from layoff) would be favoured over anyone current. Williams and Mosley would have the best chances, with Clottey next. Pac should probably box at 140 or 135. I think he can beat anyone currently there, with the possible exception of Hatton at 140 and Guzman at 135.