More to that.

I'd estimate the distance raced to be about 1/3 the distance of the total battlefield length (assuming that the Hun line is set up at approx the centerpoint). What was noticable was that the difference in speed between the cav units was not visably noticable until about half the raced distance had passed. Therefore, over short distances (1/6 total battlefield) the differences in speed will be negligible and I would suggest that the speed differences at combat distances are moot (which agrees with your observation). If CA wants to have speed differences between cav types (and they should) the speed differences need to be more exaggerated (unless there is also a 'time to react' factor which could also be used to give light cav a speed advantage).