Jordy Nelson is freakin' awesome.
If I had to guess, I would bet that on average whites peak in speed later and then slow up earlier (the latter was Bill James's finding in the 1980s about white vs. black baseball players who appeared to be equally fast as rookies in terms of triples hit, not grounding into double plays, stolen bases and so forth).
I would also guess that with whites, sprinting speed correlates more with a slender build than it does with blacks. On the playground as a kid, the fast white kids tended to be whippets. But then watching sports on TV, there seemed to be less correlation with shape among blacks. Fast blacks could come in unexpected shapes, like 1964 Olympic sprint star Bob Hayes, who went on to a pretty good NFL career as a wide receiver.
But Nelson was always documentably a terrific athlete -- a multi-event state sprint champion in high school track who is tall and strong. He's also the third string quarterback for Green Bay in case Aaron Rogers and his backup get hurt.