My high class scout doesn't seem to improve the speed by much, the pathfinder trait only gives me a 0.09 speed increase and despite having 33 extra horses and only 49 footmen I only get a speed increase of 0.12
Here's a trick I only discovered on my recent revisit so maybe it'll help you. Sumpter horses are actually fake and ghay. They're not horses where it counts and are good only for carrying your loot and eating in a pinch. In order to get an actual speed increase, you need the premium horses at the rate of 1 horse per footman. Also, you can go a bit higher than that, but if you go overboard and get like 300 horses, you'll get a herd penalty and start moving even slower.
But in general, while I'm playing on everything else realistic I just put movement speed on very easy when starting a new campaign, because I can't be bothered Benny-Hilling all across the map for days.
I never tried it, but now I'm thinking of a Bluebeard/Black Widow type playthrough where in a game with character deaths enabled you mary lords as soon as you can, get their gear, and then make sure an "accident" happens to them by sending them naked into battle with the cheapest possible party. Or alternatively, as a special battle group in your party (but I think 1.7 doesn't let you do that anymore). Then you repeat the process. Not sure how that's going to play out in practical terms, but the idea seems hilarious to me.