I really don't see the point of adding a sprint mechanic. In Warband, after you're character picks up speed when running, he automatically goes into a sprint mode.
I wouldn't call the 'jog' in Warband a 'sprint'. Unless you think Usain Bolt, world record 'sprinter' runs the same speeds as the guys in Warband, I think you may have go back and have a look xD A sprint as defined in the OED is to "run at full speed over a short distance" rather than "do the same jog you've been doing all your life only just a tincy bit faster than you used to do it".
Where do you come up with these stupid arguments? Last I checked, Usain Bolt doesn't run with 40 pounds of gear on, and a 15 pound musket. Do you expect to sprint that fast, if at all, with that gear on? It's extremely tiring, and won't last long. Again, after your character picks up speed, you can clearly see it goes from a quickwalk, to a run, to a slight sprint... It does not last as a sprint either. If you turn, or stop, you have to pick up speed again, just like any human, including Usain Bolt.