Rco spadafora sparred with Mayweather too. Ivan Calderon sparred with Oscar dela Hoya too. Infact, Calderon beat Cotto during the amateurs.
I pick Whitaker by a close decision, maybe even disputed one. It'd be a very skillful (obviously) chess-match, with Whitaker's jab and workrate being the difference. I can see much of the bout being in the middle of the ring, both guys circling and looking for the right positioning, Mayweather looking to land that straight right in, while Whitaker throws that busy right jab. Mayweather might also switch to his high guard and try to apply pressure (as he has against the speediest opponents he's faced), or get closer and dig in those nice short body shots. Unfortunately for him, Whitaker was very adept himself at fighting at close range, body punching, and knowing where to place his feet for both defense and offense. Whitaker had a bag of tricks a mile long as well. Two would be two ring geniuses going at it.
Whitaker is just better and would be to good at any range. Mayweather has been more consistent and discipline throughout his career though...If Pea comes underdone or fights half arsed like he did a couple of times Floyd most definitely beats those versions of Pea. But both at their best...Pea wins nearly everytime by a couple of points.
The JC Chavez that Pea outboxed was a pretty fearsome fighter at lightweight (although his best weight was Jr. Lightweight). I'm not sure any of the guys PBF fought at lightweight were close to being as good as Chavez. Of course that doesn't mean PBF couldn't have possibly won a decision against Whitaker. I just think PW was a bit better and probably would have won. Someone has got to invent a time machine so we can really find these things out.
Whitaker-Chavez was at welterweight (145). I actually thought Chavez peaked at lightweight, in the Rosario fight.
I'd go with Floyd. Both have superb defense and great underrated offense, but Floyd has a big edge on his ring IQ. I think Pernell was slightly faster with his hands whereas Floyd had slightly more power. I just think Floyd could do more than Sweet Pea and adapt much better than Sweet Pea.