Against Mayweather, he would have more success hitting Floyd than Hatton did. BUT he wouldn't be able to get Floyd's respect and make him back up the way Ricky did. The Mayweather of today is much bigger and stronger than 2007 Mayweather. He'd get UD'd/stopped late but he'd put up a much better fight than most people give him credit for.
He would also be more competitive against Pacquiao. His rangy-ness could get him a few of the early rounds, but i do see him getting stopped. I can't see this fight happening though...
And off course he would do better than Mosley did against both. Mosley got shut-out by both. But Shane is way past it. A Prime year 2000 Mosley would be a different story