I've had royal knights up to 14 valor before. I get my best results when I dismount them (thus giving chivalric foot knights) and put them in a woods in a battle where I know I'm going to get attacked by lots of horse and spear (i.e.- a condition where I will be able to get lots of kills with minimal losses in return).

I know being on horseback gives them a much better charge bonus, but I find that my men on horseback are very vulnerable to charging into circumstances where they get overwhelmed. Put them on foot in a battle line in woods and they get protection from incoming missile fire along with a slow speed that prevents them from running out too far in front and getting swarmed.