From my very rough estimations, armies move at about 10km/day on average... I think. All the same movement modifiers that are in play regularly still apply, relevant to the increased values now, so traits and weather and whatever else that helps or hinders movement will have its effect, including for agents who can make some nice long trips at a much faster pace which probably makes sense for solo or small groups of travelers. And generals/FMs can move across the map real well on their own without attached armies, for getting to and fro cities, handling business. It all pretty much makes sense to me, scale wise. At least, definitely more so than the scale is by default, which is I'm almost positive painstakingly slow for army march speeds compared to any numbers I've seen in what little research I did online for this. And even though I initially wanted to make this change mainly just for this reason, the realism aspect, it turned out to have a big positive effect on the gameplay itself in my opinion. Classic win-win.
Some more positive gameplay effects with how AI handled its armies included the way it attacked targets and reinforced its own forces. Even though a lot of small groups or individual units wouldn't join into single large armies, the way they would array those units all around a target was really cool, and might make for tougher battles against AI as the player I imagine (or easier, depending on how you play it). Because of how enemy reinforcements would be coming into the battlefield from all sides since a lot of times they'd move many single armies and partially surround the enemy, since they had the leeway to move and arrange units as they saw fit for the most part. And it's not like since the AI has this newfound ability to move really far, it uses 100% of the available distance all the time. In fact, most of the time it just moved armies around to key points, borders, ambush locations, reinforcements, things like that. It's just simply the fact that it was able to do this in one or two moves, rather than cueing up for several turns and having plans get interrupted and things change before they're ever able to be enacted in the dynamic campaign environment. This actually ends up making the campaign feel more dynamic, but also the AI more responsive within it, which is like a double boost of awesome.