Something I think folks are often unaware of is that the 40-yard times like the football players do in combines and "Pro Days" exclude reaction time, while the times for track races like 100 meters include it. This is a big difference in a 40 since it's at least 0.10 seconds. Anything under that is a "false start" in track sprints.
Splits for track races are always in intervals of meters so it's hard to be sure, but if you assume constant speed over the 10-meter intervals, Bolt ran the first 40 yards of his 100-meter world record (9.58 seconds) in 4.20 seconds, excluding reaction time. Including reaction time, he ran it in 4.34 seconds.
Bolt wasn't particularly fast out of the blocks (by the standards of world-class sprinters) with how big he was, he won because his top speed and ability to hold that speed were so far beyond everyone else (although he was a remarkably good starter for his size [nh]). I would bet the smaller guys have gone sub-4.20 for the first 40 yards.
I would be surprised if a non-sprinter who reportedly weighed 230 lbs ran a legit 4.12 (Bolt I think was 210 or so), but Bo was a freak, who knows.
