What this experiment completely misses is the effect of athlethics on acceleration, the most important aspect of movement speed, at least for melee. In my experience a full strength guy is not all that much slower top speed compared to a high agi build. But when you start taking turns, side stepping and moving forward and then backwards, then you will notice a huge difference caused by athlethics. As a full strength in plate you can't even stop immediately, your character will slide onwards a bit after you stopped pressing forward. Acceleration is so much more important than top speed.
Also, I can not quite agree that a 10% speed difference is insignificant. It means that you get a meter distance every 10 m from the other guy, which means you easily outrun him. Also that the guy without athlethics has 3 more agility reduces the accuracy of the experiments, as agility affects movement speed as well. To truly estimate the effect of athlethics you need to have characters with the same agility.
In any case, here is a thread with extensive testing on the subject by WaltF4 for those that are interested, he knows his shit. Sadly his testing does not look at acceleration either.
http://forum.meleegaming.com/beginner's-help-and-guides/running-in-crpg/