It has no thrust, so it has 0 thrust damage. Also, do not consider knockdown much of a factor that you need some power strike to make it happen regularly. Speed bonus will surely help, but do not rely on knocking your opponents down if you have 0 ps. It will not happen for the most of the time.
Blunt is a good choice against armor, rather than pierce. Pierce is better if you have a high damage, blunt is better if you have lower damage. Go for military hammer, I will do it with my same pure horse archer as well (level 30 currently).
However, if you are a pure horse archer you better use your bow as much as possible. Even at closer range, you can bump shot people which will help your teammate and use your melee weapon only if you have no other choice. Otherwise, you might want to try Jackie's hybrid horse archer build which seems extremely good. It also allows you to have a shield, but I think it's not the thing you're looking for. So, you might want to focus on a build that allows you to have 5 power strike at level 32 if you feel like going for it.