Smooths build is fairly good, however u stated you wanted destriter, and its definitely the better horse for 2h cav as your more up close and personal than ezmode lancer cav were u can stab someone from far away out of harms reach and ride off before they can attack back. I altered smooths build only a little, basically what you have here that is differnt is -3 agility, -1 riding for +3 strength and +1 power strike. Power strike is more important than riding skill you dont need and the strength which you would need anyways still gives +1 hp doesnt it? Anyways using a longsword you need all the PS you can get, especially as 2h cav. Once you start getting up there in powerstrike you can kind of think of it as maybe at 6PS i can one shot 35% of players, at 7 55%, at 8 75% at 9 85%. Thats not really accurate as i dont know especially with longsword, but it does work that way in general.
As 2h cav its extremley important that you one shot your opponents becuase if they survive and they know your trying to kill them its very hard to kill them as anyone, even a 1 hander can dehorse you before your even in range to hit them, unlike easymode lancer cav which could kill a 2hander before they have the chance to hit the horse. So 1shotting people is the most important thing, and also the IF is nice as horse is expesnive so you typically dont wear really heavy armor. 5 Athletics is enough to still be effective (especially if your in light or medium armor as most cav are). And also the PS really helps in strat too. The 120 2h might be just a little slow which is one of the reasons i use 1h but should be ok if your good at 2h.
EDIT: Oh lol my build is smooths troll str build.
Strength: 27
Agility: 15
Hit points: 76?
Skills to attributes: 8
Ironflesh: 7
Power Strike: 9
Shield: 0
Athletics: 5
Riding: 5
Horse Archery: 0
Power Draw: 0
Power Throw: 0
Weapon Master: 0
One Handed: 1
Two Handed: 120