Sorry for necroing this thread. StonkZ11 proposed a good one here.
Stable techs gives 50% more attributes.
I think this will be an OP bonus. Hussar will have 120HP and 12 attack. Paladin will have 220HP and 20 attack. Both of them seem to be OP units. Also in castle age, cavalry will move 15% faster. This can also be a bit OP as Cumans bonus is kept at 10% in castle age instead of 5% as a bonus + Husbandry.