Re: Floyd vs JMM at 140. Would you buy it?
Floyd would never go down to 140 lbs to fight Marquez, he would make Marquez come up. And it's clear that from the first Floyd vs Marquez fight that he was willing to lie on TV and come in at the weight he wanted anyway, so even if Floyd said he'd drop to 140, he would be at whatever weight he wanted come fight night which would not be 140 lbs.
In an alternate reality where Floyd wasn't like that and actually would make 140 safely, I doubt it would make much difference in the fight. It's a terrible style matchup for JMM that forces him to play the role of aggressor instead of his natural counterpunching role, and while he can do that against a lot of fighters, Floyd's defense and edge in athleticism is just too much for him to overcome. He'd be more competitive than their first fight but probably not much more.