We don't know. He may as well be very fast but we can only see his acceleration, which is really good by the way. He would probably get tired after 300 yards though
I read somewhere that Chimenti was a trackstar at highschool, and that he is still able to do a 100 metres below 10, 80. So I guess Chimenti is our fastest player.
As for the slowest; Emerson?
Well,if you watched Ars-Bayern games,then you saw that Kovac managed to catch up Henry....in couple of occasions.... I doubt many of Juve players are capable of that....