The pound for pound title has no specific formula and is strictly based on opinions and your like or dislike for a specific fighter, fighting style etc so everyones opinions on the subject will differ. This is my take on it:
Mayweather today is ranked #2 P4P and only lost the #1 P4P rank when he retired. In his last fight he beat Marquez who was ranked #2 at the time when Mayweather fought him. Mayweather is now going to fight Shane Mosely who is ranked #3 on the P4P list.
Pac in his last fight was ranked #1 P4P and beat Cotto who was ranked #17 P4P at the time. Pac is now about to fight Clottey who is currently ranked #34 on the P4P rankings.
If both fighters win their respective fights keep in mind that Mayweather would have beaten the #2 and #3 P4P fighters in the world back to back while Pac would have beaten the #17 and # 34 P4P fighters in the world back to back. I would give Mayweather the nod to become the #1 P4P fighter in the world if both fighters win their next respective fights.
Mayweather today is ranked #2 P4P and only lost the #1 P4P rank when he retired. In his last fight he beat Marquez who was ranked #2 at the time when Mayweather fought him. Mayweather is now going to fight Shane Mosely who is ranked #3 on the P4P list.
Pac in his last fight was ranked #1 P4P and beat Cotto who was ranked #17 P4P at the time. Pac is now about to fight Clottey who is currently ranked #34 on the P4P rankings.
If both fighters win their respective fights keep in mind that Mayweather would have beaten the #2 and #3 P4P fighters in the world back to back while Pac would have beaten the #17 and # 34 P4P fighters in the world back to back. I would give Mayweather the nod to become the #1 P4P fighter in the world if both fighters win their next respective fights.

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