Ok, I've seen numerous calculations and such about what Usain Bolt would run a 40-yard dash in. Some are insanely low (sub 4.0) and some seem really, well, slow for the WR holder (4.33).
Simply taking his 100m time and stopping at 40 yards doesn't do it, there is his reaction time to the gun factored in there. Whereas NFL electronic time starts on movement.
This yahoo article brings up some interesting points on why you can't do this. ie Bolt gets starting blocks, accounting for movement vs reaction to gun etc...
Some links to guesstimates of his times:
I am sure someone out there smarter than me can solve this riddle. How fast would Bolt run an NFL style, electronically timed 40-yard dash?