That doesn't mean they can't turn and run, it's not like Wr just run go routes all the time, that's why change of direction, hips, and quickness are more important than just straight line speed. That being said, majority of CBs in the nfl run in the 4.4s and Miami has multiple CBs right now who can run in the 4.5s some even faster. The ones that probably run lower than 4.5s are Bandy, Bethel, and Couch, Blades and Ivey run in the 4.5, the only one that you might have to worry about speed is William's, he ran a 4.6, but that was a while ago.