As far as i remember (it's been a while) there is a clumsy hardcode of cavalry speed:
It checks unit armor. If unit has what editor refers to as 'mounted armor', then speed is hardcoded and equals to infantry speed 7 regardless of what you set in Mv.
But you can make cavalry type, non-zero mount byte (horse or boar), just set them regular armor: 0 through 4. Then you set mv = 9 (for wolfriders) and they run fast. Ijust hope that no 'mounted armor' does not prevent such unit from being a cavalry in all fight checks. It works properly in ctl though and no reason to suspect worse at lower code levels.
Addon: mounted armor may influence certain combat situations, like polearm infantry cancels its bonus or something like that. But there is no other choice atm to make faster or slower cavalry.