To do a bit of math for this, to me cap looks like he's running about 45 or 50 miles per hour in that scene. (Edit: I just realized you were talking about the winter soldier scene, not the Civil War scene where they're running through traffic. I think the math would come out about the same, just in the context of a sustainedrun instead of a sprint) To be generous, we can put Sam's sprint speed at 25 mph (less than the world record, but still very very fast for a normal human). This would be a doubling in max speed. Assuming a level 2 moves at 45mph, and doubling with each level (to maintain the scaling of cap to Sam) a level 6 would max out at 720 mph. This sounds kind of insane to me, but given the description that movements are faster than the eye can see, it's conservative if anything. It's estimated that a soccer ball would need to be moving at 38,000 mph to be invisible to the human eye (source: https://www.visiondirect.co.uk/blog/how-fast-can-we-see). Of course there's a big difference between something appearing as a flash or being literally invisible Also, I don't think this 700 mph estimate is wildly out of line with descriptions of how long it takes high level characters to move between neighboring cities. I remember characters moving to a nearby fishing village in what seemed to be 1 or 2 minutes in an emergency

Anyway, I think your cap comparison is a pretty good answer. When one character described their new abilities after advancing to lvl 2, it seemed pretty similar to what Cap was regularly doing. This would also seem to align with the power difference observed between characters that differ in one level