Jerry Rice ran a 4.71. No i'm not saying he's Jerry Rice, but it's a single metric.
Pull out your phone and try to stop the stopwatch at .3 of a second. That's the difference between 4.81 and 4.51. Now imagine extrapolating that over 40 yards. .4 of a second is literally less than 1/10th of the overall time.
There are a lot of things the 40 time CAN tell you, but it's also become a massively over-stated metric that I think has let really good players be under-valued. Straight line speed is not anywhere near the most important part of an NFL players metric. in fact i think it's borderline comical that Oline and Dline even run a 40 yard dash, as they NEVER have to be at full speed for 40 consecutive yards. When i mentioned the 'Ouch' in my post earlier, it was because of the optics, not because of the actual measurement. The more 'concerning' metrics are the agility measurements like Shuttle, Vertical, and 3 cone, as those are going to be measuring ability to separate in small spaces. A lot of DBs are faster than the WR they cover, but the WR can still create that separation to flash open and allow for a QB to make a throw. It's not very often that you see a WR and DB running 'straight' with the WR pulling away, that's not how offenses are schemed up because it would never be truly successful. Leverage, being able to get a DB off their mark, and deception are 100000% the most important part of it. Being able to outrun them is not. It's a benefit once they have the ball in their hand, that a guy can create an explosive play, but it's still shouldn't be an absolute.
I wanted to look at the actual math and it actually supports my thinking
a 4.81 in the 40 yard dash run over 100 yards means it would be 12 seconds
a 4.31 conversly would be 10.8 seconds.
That means over the course of 100 yards, the guy who runs 4.31 would only be 1.2 yards (roughly 4 feet) ahead of the guy running the faster time. The same logic applies the other way. If the WR who runs a 4.81 catches the ball with a 3 yard cushion, it would take roughly 250 yards to catch the WR. Of course there are other aspects of this.. what is top speed vs acceleration? If the 4.31 guy can get to top speed faster, but top speed is slower than the WR, he would never actually catch them, but would test better in a shorter metric. If the WR has better acceleration creating the separation, but the DB has a better top speed, then he would be able to catch that WR because of that. This is where Darrell Green, and others have been truly elite. They get to speed fast, and that top speed is fast. That is the exception, a guy who can not only test well in short bursts, but can maintain.