@ JRTomlin
I agree; I do think though that "well fed and well conditioned" are operative words, IMO. In the preindustrial era, you needed to either haul your feed with you or travel between places where you could obtain it to make much better speeds than that. I concede, riders, traveling between well-established points could easily travel 50-60 miles in a day, because feed was available along the way or at the destination. Alternately, if you can carry enough feed to keep a mount well fed, without unduly sacrificing a lot of weight, you can also travel much further than if you can't carry the feed or don't have it. Things change if you need to forage or graze, though.
It's not that different than how fast a pre-industrial army could march. The average daily march during the Napoleonic era, including the US Civil War was around 17 miles a day. There are always going to be exceptions. I recall one brigade/division that marched 50 miles in one day during the civil war, but that was very much an exception, and earned that unit the nickname of foot-cavalry. The major limiter of that time was an army could really only move as fast as their logistics train, which tended to be slow.