Clock time is interesting. I'm not sure how much of an indicator it is of actual speed.
I wish there was a way to measure acceleration from standstill, acceleration while running, acceleration in and out of cuts, etc. I would say these things are more important than straight ahead speed. For example, Wes Welker ran a 4.65, but man is that guy friggin quick from the block, and quick in and out of breaks.
Then there's the "second gear" people mention. Can someone be running full speed and then kick it up for a pace or two? Some can.