I think Mayweather beats them both, and before people say I am nuthugging which is inevitable I will state my case.

Why Shane lost: Obviously there were other factors, but the biggest one is that Shane thinking he was the stronger guy in both cases simply didn't box well enough against either. Instead of using intelligent movement and guile, especially against Wright he simply tried to bang away. Against Forest he didn't use his jab hardly at all, he was leaping in from way too far away with big punches, a lot like Berto. Forrest saw everything coming a mile away.

Why Mayweather would win:
Against Wright: Even though WRight was older I think his fight against Bernard is evidence that highly intellectual defensive fighters can take away Wright's arsenal. I think the speed difference would be great enough that it would compensate for the age and size factor between Wright and Hopkins(I think Hopkins was still a little fresher when they met). I think Floyd would stay out of range, lead with a right hand that would sneak through Wright's guard than either move away at an angle or clinch. Once again MOsley's inability to block the right hand and his unwillingness/inability to box moving backwards effectively made him an easy target for Wright who kept him at range with the jab, I think Floyd wait for that jab and stay further away and counter off it all night long. I think Floyd would make this an ugly fight where Wright wouldn't be able to get punches off and he would be frustrated by Floyd's movement all night like he was against Bernard who kept one step ahead of him.

Against Forest: I think Floyd would use his superior speed and boxing skills to outjab Forest and beat him in a way similar to how he beat Oscar, I think it would be a more competitive fight in the middle of hte ring, but that Forest wouldn't be as effective in back Floyd up or at throwing combination like Oscar did. Vernon was a really good A- fighter who had the perfect chemistry to beat Mosley, but he wasn't a truly complete fighter, and I think as the fight progressed Floyd's superior skills would play a bigger a bigger role as he would gradually take over the fight down the stretch.

Wright is truely a great fighter, but both he and Vernon were so effective against Mosley because of how Mosley fought against bigger technical fighters who were quick enough to deal with his speed. He didn't use an intelligent formula to fight either of them, and I think Mosley's style simply wasn't meant for fighting guys who were bigger and stronger than him. The only reason IMO he beat Mayorga and Vargas(at least the first time) is because they were so much slower than him, but even including them he hasn't been effective at all against larger opponents except Margarito. Who was IMO just a taller guy who lacked speed or any sort of strength advantage over Shane.