I've never used straight movement speed as the mechanic for chase scenes, because that only takes into account straight out speed. And when it comes to chase scenes its never just about speed. Classic chase scenes include checks regarding endurance (CON), knowing the proper/faster directions/places to run (INT), jumping over and around obstacles in the way (DEX), putting things between you and the person chasing you (STR), and even convincing others to help slow people down (CHA).
As a result, I run chase scenes more as skill challenges than anything. I'll use a typical narrative distance line (Close / Near / Medium / Long / Far / Extreme), choose the point where the two are in relation to each other (say the chaser is at Long distance currently), and then as we narrate the chase and the player says what they do as they run, the checks can be used to close or extend the distance between the two. The chaser needs to move up the line to Close, the escapee needs to drop down the line to Extreme, at which point the chase has ended. Direct movement speed usually never comes into it (except in the times when I've narrated an open straightaway and the player says they go into full sprint mode, at which point a STR (Athletics) check will come into play and the player might get Adv or Disadv depending on if their movement speed is higher or lower than the other person in the chase.)