Most of the time in football player are using functional speed so they can stop, start again or change direction with out serious injury or wear and tear on the body.
So that seem to make a case for 2K. I keep hearing about NHL system of speed and sounds better suited for football games then what both 2K and Madden uses.
I dont know why people think its a accurate system for speed to just hold the sprint button to get to top speed. Its rare to see people sprint if there not in the open field.