Mayweather doesn't like to fight speedsters, go watch the Zab Judah fight. He was getting his ass kicked until Judah had is usual blow out after the middle rounds, he's also a southpaw.
Not sure id class Pacquiao as a speed merchant,there was a time a few years back when the speed and reactions of his footwork were as quick as anyone id seen and thats something i would have given him a chance with but what ive seen of his last few fights thats nowhere near what it was......He,s a crisp accurate puncher but nowhere near as quick as someone like Khan who i think can give Mayweather more prob