Mayweather hasn't put on 6 pounds for a fight since he was at 130, I can't see him doing it, he makes 143 too easily, and he trains all the way up to the fight. He's faster physically, but Mayweather has been fighting slower guys, and obviously Marquez can deal with speed. When Mayweather fought at lightweight he also weighed 140 coming into the ring, Marquez could easily put on more muscle and still be fine speedwise, I can't see him weighing only 140, and even if he did, it only helps him to be lighter against Mayweather.