21/18 is an extreme pure cav build. You need to give up on a lot of skills, it can be difficult to play sometimes but i like it a lot.
Next retirement i will try this, now i have a little different build (this one is for lvl31 while now i have a lvl30 build)
    * Strength: 21
    * Agility: 18
    * Hit points: 70
    * Skills to attributes: 6
    * Ironflesh: 7
    * Power Strike: 7
    * Shield: 0
    * Athletics: 0
    * Riding: 6
    * Horse Archery: 0
    * Power Draw: 0
    * Power Throw: 0
    * Weapon Master: 6
    * Polearm: 157
This one is more a heavy cav build with heavy lance, backup polearm and a slow horse, but can used effectively also by a light lancer.
Heavy lance is slow as hell so you need to put all your wprof in it. If you want to do the 1h/pole hybrid i suggest using a light lance or a lance. 
With so much prof you can also use effectively the heavy lance with heavy armour.
No shield, so i can bring an hafted blade or some other 2slots polearm. Also no Ath so i can put points in IF wich is good, without shield you will take a lot of arrows.
6 Riding is also nice and you can see it's faster then 4 o 5 riding, especially when climbing hills.