There are two types of muscle fibers - fast twitch and slow twitch. Slow twitch muscle is beneficial to distance runners. They fatigue slowly and are better for distance runners (CBs) and WRs who are striding down the field all the time.
Fast twitch muscles are what DTs and DEs need to get off the ball quick. They are best for short bursts of speed.
DEs and DTs use fast twitch muscles.
Info on muscle types.
Basically, I'm trying to say that bench press, 40 time and other crap mean ASS when it comes to evaluating a player. It is all about muscle type, and how your body works on the field when you have yourself loaded with equipment.