There's a funny asymmetry in the way we deal with numbers. Dividing is tricky; you often have leftovers and have to deal with rounding and it's just a slow operation. Multiplication is relatively easy.
Maybe it makes sense to reframe the "normal" wilderness movement speed based on wooded hills, sort of the default background terrain for D&D unless otherwise specified, and then have multipliers relative to that baseline rather than setting speed based on the best possible terrain, flat plains, and then dividing.
In ACKS, wooded is x2/3 and hills are x2/3, so if you are in wooded hills you multiplty those and get 4/9 which is close enough to 1/2 for government work. Which, conveniently, is also the speed multiplier for mountains, swamps, and a variety of other terrains.
So then this looks like:
- 120' speed -> 12 mi/day, 2 hexes
- 90' speed -> 9 mi/day, 1.5 hexes
- 60' speed -> 6 mi/day, 1 hex
- 30' speed -> 3 mi/day, 0.5 hexes
Being able to just divide speed in feet per turn by 10 to get miles per day is pretty nice; it's not that the arithmetic was tricky before, but 10 is a super-easy constant to remember. Riding a medium horse with 180' speed? 18 mi/day, boom. And as long as combat speeds remain multiples of 30', wilderness speeds will remain multiples of half-hexes.
Then if you're on a road, or in flat clear terrain, multiply by 2. If both, multiply by 3.
The 9 mi/day is a little annoying, but "three hexes per two days" isn't too bad.
Forced march is also a bit annoying, since multiplying say 1.5 hexes per day by 1.5 gives you 2.25 which is not a multiple of 0.5, but I suppose one could go with "cover two days' distance in a 16-hour marching day, then have to rest for two days"?
Having a table that handles rounding or dropping fractions could also be a reasonable approach for dealing with odd situations like "we have 90' speed and we're forced-marching (x1.5) through scrub hills (x1.5, if you wanted to re-introduce the increased speed for not having the forest penalty), we move 3.5 hexes". Or just don't worry about it and find workarounds that let you multiply by 2 instead.
Flying also becomes quadruple speed instead of double, since speeds were halved.
I think I like this proposal a lot more than my movement points idea. Sure, it loses some detail (doesn't distinguish between hill forest and flat forest, for example), but ultimately... I'm not sure that's worth worrying over. Differences in terrain speed make computing optimal paths more annoying, but if you don't show your players the map of the wilderness, they can't compute optimal paths anyway until they've been there and back and done some exploring. So you shouldn't be losing too much gameplay here, and what routing "gameplay" you are losing wasn't really fun, so... sounds fine?
And returning to the wilderness as dungeon metaphor, I guess instead of using soft-walls of slowing terrain types where you have to stop and think about routing all the time, you can instead use hard-walls like impassable ridgelines and rivers to break up "rooms" and only occasionally include slow and fast terrain to mix things up. Just like in dungeons, where most dungeon floor is just... floor, with standard speed, separated by walls.
Having 12mi/day as the standard is also pretty close to Arneson's 10mi/day (thanks for mentioning this, DHBoggs!).