As a group, warm weather schools, and southern schools in particular, field better football teams than northern ones do. There are plenty of data to support this assertion: SEC was 7-2 in bowl games; more players from these schools goto the pros; the majority of highly ranked recruiting classes are at these schools, etc...

Better players, are generally faster players. Therefore, it is not a stretch to say that souther schools have faster players.

What I think is more interesting is the trend toward warmer-locale football dominance. I believe this trend has less to do with a decided speed-focus (the coaches are nomads and all go after the same players) than the fact that great players like warm weather locations. High schools seniors, it turns out are being drawn to the Sun Belt just like everybody else.

Think of a top-ranked recruit from St. Louis deciding between Michigan and USC. One place has better weather and prettier girls. Michigan is already a step behind...

Gee I guess we just ought to draw the Mason Dixon line across the USA and have separate football leagues. There has been a current trend but hopefully a northern team will make you eat your words soon enough. :P