Wow, so far we have Pac knocking both prime Duran and prime Chavez out at their best weights. Gets beaten by a 40 year old lightweight, can't knock out a weak punching Bradley or a 40 year shot to **** Mosley, but he stops prime Duran and Chavez? Ok.
Anyway, the speed wouldn't be as much of a factor as people think. Against guys who can slip and counter very effectively, and get inside using angles, rather than just standing in front of him, Pac gets lost, makes too many mistakes and just gets hit too cleanly. Chavez's defense very underrated as was his ring savvy and countering.
I think he hurts Pac to the body and really has a big effect on him that way and takes a close, but clear decision ala the first Morales fight.
Add this to Chavez' obvious offensive, power, countering, and other skill capabilities.
How quickly people forget.