It depends largely on how Williams chose to fight, I think. Against Sharmba Mitchell, Williams walked in whenever he felt like it because he wasn't threatened by his power. Had Mitchell had some oomf to his blows those three left hooks he hit Williams with would have staggered him. But against Margarito we all saw the flurry of punches he threw all night. I think the Margarito version would be problematic for anybody. He could reach across the ring and tap Mayweather and he has a decent inside game. Williams' only major problem is once Mayweather got inside he could ring that chin like a church bell at noon. One of the things Mayweather breaks opponents down with is a body attack and he can use Williams' high workrate against him by utilizing it.