QB's, backers and defensive linemen is where I put my interest. Those 4.2-4.4 types, it's all about the day/condition they are in. They have speed. I will say this, those with actual track experience will maintain their speed longer (talking seasons) than just some quick 40 guy. I would look for that but I do doubt football people think that way, it's all about...the right now.
As we'll see in this edition of the NFL combine more and more QB's in that 4.55-4.65 world, as speed at that position becomes moire important, yep....evolution
A big guy with some serious jets, valuable!