Quote Originally Posted by Turin
It's not bugged so much as gimped. At very high values, charge bonuses do seem to have an effect.

All in all, it seems that it is the weight of the horse that matters the most.

From what I understand:

Light horse: least charge effect, fastest speed
Heavy Horse: medium charge effect, medium speed
Cataphract horse: greatest charge effect, slowest speed
Actually, it is armour value that determines charge effect, not mass (though it does play a role). It was discovered in this thread, which, for some reason, never made it to the Ludus Magna: I bet you don't believe this: cavalry charge is broken.