It would be similar to what happened against Lara. Tall Paul is just too open for counters and it’s not like he has the power to really bother Mayweather. It would be a pain in the ass, but Floyd definitely beats him by a clear decision.
IMO this would be similar to the first Maidana fight where Maidana would be throwing more punches while Floyd lands the cleaner shots. Williams would have presented a more difficult problem but would still be getting hit flush in return. Mayweather would edge it in a close fight.
I always thought Williams was a terrible style matchup for Floyd, being half a foot taller with a crazy workrate. But Williams also had terrible defense. I think Floyd would use a lot of good movement and frequently catch Williams down the middle, and tie him up to disrupt his rhythm. Williams would get some rounds due to his activity, but not enough. Probably another 8-4 type decision for Floyd.