I find my self stressing this one single point.
We will not be able to fully comprehend the games mechanics until release or until there is a video release showing every angle of the games physics [A man can dream?]
This is true.
BUT, we CAN work from the information we've been given so far.
And, BASED ON THAT INFORMATION, the characters will have movements speed which is altered ONLY by their body type, and not their weapons.
This may prove incorrect after release, but if it does, that's because we've been deceived.