That's the build that I'm running right now, and I'm fairly happy with it. A note on survivability: have you considered running a shield? It would mean taking a crappy 1-slot polearm as a sidearm or getting 1H proficiency and a weapon, but it helps a lot with keeping you and your horse alive. I missed my shield this gen.
My plan for next gen:
Strength: 18
Agility: 18
Hit points: 59
Skills to attributes: 2
Ironflesh: 3
Power Strike: 6
Shield: 2
Athletics: 6
Riding: 6
Horse Archery: 0
Power Draw: 0
Power Throw: 0
Weapon Master: 6
One Handed: 129
Two Handed: 1
Polearm: 106
Archery: 1
Crossbow: 1
Throwing: 1
A couple points:
- Most of your mounted damage comes from your horse's speed, so trading one power strike for one riding won't cost you very much.
- 6 riding would at least let you try a Courser. Finding a Champion Courser and taking it for a spin is something everyone should do at least once. Those things travel at around Mach 2.
- If you do decide to forgo the shield and go pure polearm, consider the Fauchard as a secondary. It's damage isn't huge but it's fast and long, things that will ward off enemy lance cav if they down you and come back to try to kill you. The lower upkeep will also let you ride your horse more often!