Deshavi is a great choice for path-finding if you're going to be a "good" guy. Borcha is the "evil" tracker. I don't think inventory has anything to do with speed, since I go just as fast with 3 of every food, about 12 squares of gear (siege gear, khergit combat, regular combat) and the rest filled with weapons and armor (plunder, not gear) as I do with none of the loot and almost none of the food.
I hate Khergit veteran horse archers, and I don't just mean fighting against then, but using them in my army. They are nigh worthless, in my opinion. Sure, they might kill some guys riding around and shooting their arrows, but they take -forever-. Battles in which I am fighting alongside or against Khergit veteran horse archers take about twice as long to complete because they're running around like chickens with their heads cut off, plinking away at heavily armored troops with those weak ass bows.
I use lancers, however, because they try to stay within a distance they can use their spears in. The horse archers just draw a bunch of mounted units after them to the other end of the field and do a handful of damage to one or two of them.
If you use an optimal hero build with 7 heroes (the most you can have without any dislikes)
I disagree with this, or at least I'd like you to define "optimal". For instance, Ymira and Matheld don't get along, and while they both are "apalled at my choice of companions", they stick around. Only once has Ymira threatened to leave (I had to persuade her back) and that was after I took a -severe- morale hit. I was negative some obscene number, if I recall. Otherwise, I've never had a problem.
Matheld, Bunduk, Nizar, Artimenner, Ymira, Deshavi, Katrin, and Marnid all get along fine, with the notable exception of Ymira and Matheld who, if you side with each of them one time in their arguments, will remain with your party.
I do agree about the trainer skill, though. Most of my heroes have one point in it, though Bunduk has like 5 or 6 points. That skill is absolutely necessary if you are planning on keeping control of more than a few fiefs, especially large towns.