3-4 HA is a huge difference. At 3 HA you are a trot shooter. AKA an archer on a horse. You can't act as fire support for friendly cavalry, and cant outshoot horsearchers in a moving firefight. even worse, you can't pin down enemy foot archers (note plural) by dodging and shooting at the same time while they are forced to stay still to even hope to hit you. If you think horse archery is an archer that can quickly redeploy, then HA 3 is ok. If you even want to try shooting while moving, HA 4 is minimum.
Since the level of HA is a defining factor, I wonder why you went for a khergit bow, while adding points to IF of all things. HA 4 gives you a strongbow, HA 5 forces you to use a nomad bow. HA 3 is a trot shooter.
Having used both builds, here are the differences. With nomad bow, you shoot like a dream on horse. Scoring horse headshots versus enemy cav is something you can do consistently, lag willing. With luck you can even go for moving headshots versus enemy cav, esepcially those that chase you. Unfortunately base damage is very low, so the only kills will be the ones already wounded, or those you get from headshots. Fortunately, you can dehorse the entire cavalry arm since most horses have comparatively low armour. Any armour kills this build. in fact, around 20k of armour is enough to ignore your shots, unless you gallop towards the enemy while he is running towards you. Given that you can spend around 30k for this HA equipment, it is pretty bad news to see anyone with armour, let alone the people with full lordly plate. So concentrate on sniping archers from their blindsides, pinning them if they see you, and dehorsing and killing cav. Don't bother too much with tin cans.
HA 4 with strongbow is not as good in cav shootouts. I find headshots to be a lot more luck based than HA 5, so I tend to aim in a general area rather than bothering for head hits. However, you can actually start staggering tincans with this build, and can prance around shooting stationary foot archers from a good distance, which is more to your advantage since you can dodge a lot more than he can. I myself get slightly more kills using HA 4, but I feel I do less for the team, since I am unable to dehorse as many enemy cav. The fast firing nomad makes cav shootouts easier as you can quickly adjust to the fly, although strongbow can often do 2 hit horse kill.
As the devs in their infinite wisdom, have been following a trend in reducing ammo, in effect buffing 2 hands, it seems the HA 4 build will allow greater damage potential, since you can expect to miss alot when shooting while moving.
Horse archers are very fun to play as they really bring the combined to combined arms, adding yet another threat dimension that the enemy team has to deal with. Plus unparalleled kiting potential, and the ability to cause a lot of misdirected anger. Plus the look on the pikemen's faces when they brace for friendly melee cav, then get hit by you is priceless.
