Ok, so, I thought about it, and having horse archers on the same horses as knights is less than ideal! Also, I've been concerned about the maneuverability of horses for a while, as well as their inability to knock things over. So this is going to be a general horse rebalance rather than just a change to the armored horses. In general, horses will be faster, less maneuverable, better at knocking stuff over, and more vulnerable.
edit:
The first rule is that no horses will have armor better than 30. Plain and simple, horses are no longer going to have better AL than friggen Black Armor.
I also moved away from an explicit tier system to one based around horses being either fast or survivable (but not as survivable as in vanilla). The quick ones are cheaper and more abundant, to make up for the fact that they'll probably die more frequently.
And finally I moved the stats to numbers divisible by 5, mostly for my own sanity. The modifiers (heavy, spirited, retarded, etc) will provide the minor variation. TBH, I wouldn't touch the positive modifier horses, as they're way more likely to get taken down (due to their lower armor) than in vanilla, and thus much likelier to be crippled and thus lose their modifier when they're healed in your inventory.
I'll be testing these in my version, will upload as a 3.5 version in a day or two.
Armor Based Horses
Warhorse:
Warhorses are the crap version of Chargers in Vanilla. I'm changing them to be the slower, more defensive option. They'll also have slightly better maneuverability, but it'll be nothing to write home about. Knights will ride these.
Base AL of 30 (from 40)
Base Speed of 40 (from 39)
Base Maneuverability of 30 (from 41)
Base Charge of 50 (from 2

Base HP of 160 (from 165)
*Base Abundance of 40
*Base Price of 2000
Charger:
Chargers strictly dominate warhorses in Vanilla. I'm changing them to be the faster, heavier hitting armored option. To balance things out, they're less maneuverable and have lower armor. The Cataphracts will ride these.
Base AL of 25 (from 5

Base Speed of 45 (from 39)
Base Maneuverability of 25 (from 44)
Base Charge of 60 (from 32)
Base HP of 160 (from 165)
*Base Abundance of 40
*Base Price of 2000
Courser:
These guys aren't being designed for any specific unit so much as the player. They're not as highly specialized as the steppe horse, and are intended to provide a more well rounded (but speedy) mid level lancer or horse archer choice. As with the Steppe Horse, they're intensely vulnerable to attack, and should probably be used in an anti-cavalry role -- for anti-infantry purposes, use one of the other two tier appropriate horses
Base AL of 20 (from 10)
Base Speed of 55 (from 42)
Base Maneuverability of 40 (from 50)
Base Charge of 40 (from 12)
Base HP of 140 (from 110)
*Base Abundance of 40
*Base Price of 2000
Speed Based Horses
Hunter:
These guys are the vanilla "light warhorse". They're being slightly changed, but they already work pretty well for the Swadian Horsemen whose primary mount they'll be.
Base AL of 25 (from 1

Base Speed of 45 (from 43)
Base Maneuverability of 35 (from 44)
Base Charge of 30 (from 24)
Base HP of 120 (from 160)
*Base Abundance of 70
*Base Price of 1000
Sarranid Horse:
These guys are pretty irrelevant in vanilla. The Sarranid Horsemen who ride them (in this mod) use lance and jarid to attack their foes, and scimitars to defend themselves on foot. They need a horse that has some maneuverability, but they're mostly interested in it being quick and hitting hard when it gets to the enemy line. So, basically, like the chargers the Cataphracts ride, but faster and lighter.
Base AL of 20 (from 10)
Base Speed of 50 (from 43)
Base Maneuverability of 30 (from 43)
Base Charge of 40 (from 16)
Base HP of 120 (from 120)
*Base Abundance of 70
*Base Price of 1000
Steppe Horse:
Steppe Horses are designed for the Khergit horse archers who will ride them. They'll be especially vulnerable to damage, so that foot archers can bring them down without much difficulty, and their charge will suck so that infantry acts as a serious barrier. But they'll also be fast and maneuverable, so that they can ride circles around the heavy cavalry of the other factions.
Base AL of 15 (from 10)
Base Speed of 60 (from 40)
Base Maneuverability of 45 (from 51)
Base Charge of 20 (from

Base HP of 100 (from 120)
*Base Abundance of 70
*Base Price of 1000
Bad Horses
These horses are suckitude defined, and aren't actually supposed to be used for anything other than being on while you're killing looters and need to save money, or sticking in your inventory so you can haul crap faster as a merchant. The bandit units will only use these horses. They all have the same stats so the different varieties are really just flavor -- I mean, come on, sumpter has the same meaning as pack horse, and the desert horses sound like random starving crap you find wandering the sands anyway.
Saddle/Sumpter/Desert
Base AL of 5 (from 10)
Base Speed of 35 (from 43)
Base Maneuverability of 25 (from 43)
Base Charge of 5 (from 16)
Base HP of 80 (from 120)
*Base Abundance of 100
*Base Price of 100