Here's some more info from a dev blog:
HOW SEVERE COMPARED TO WARBAND; WILL MOVEMENT PENALTIES FOR USING HEAVY ARMOUR/WEAPONS BE?
“In multiplayer, we tie movement speeds to the class rather than weapon weights or armour. This enables us to, for example, make a berserker very agile, even though his weapon may be very heavy ... These speeds, as well as, the acceleration can also be set for each individual multiplayer class, giving designers (and eventually modders) an easy way to create unique classes without having the hassle to cross balance the weights of the armours for every small change.”
I noticed this in one of your videos:
Styo: "We aren't going to have an issue with tiny men as archers that can out run everyone again in Warband beta days, are we? Man, that was a pain to deal with."