I wouldnt have Floyd in the top 5. YOu never seen Gamboa or Berto yet? They are the fastest punchers.
My vote goes to Pac. My case in the video below. If you disagree, please post Mayweather video to counter. This should be interesting. http://www.youtube.com/watch?v=qKPDeMXiJHc
I would say confidently Mayweather back at 130, 135 MAYBE even 140. He was blistering. At 147 and 154 I'm not so in awe of his speed, its still right up there, but Manny's seems a little quicker to me. Mayweather may well have the superior timing and positioning which makes all the difference over a slight advantage in hand speed.
Floyd has faster reflexes in ducking punches and bobbing but handspeed (especially combos) and footspeed belongs to Pac.