If you really want to test whether or not athletics increases your top speed, you'll need two characters, one with a high (let's say 30) agility and 10 athletics, and one with 30 agility and 0 athletics. Start the timer at a given spot while they're both at full sprint. If you time it from when they start running, your data will not prove anything because athletics increases acceleration.
I'm far too lazy to do this myself, and don't feel like figuring out a reliable way to record the data accurately. I just like setting my agility to 1000 or something in singleplayer and zooming around like The Flash, or setting my strength to 3000 and hitting the damage cap with punches. This isn't as much fun.