Well, LK has made a big start on this by modding his additional units There are now regional variations on units available for most of the factions. So, maybe you should have a look at these before changing the standard unit's stats. Generally, CA made these units with playbalance in mind. They wanted each faction to have units to fit into their "rock - paper - sissors" approach to warfare, i.e. an anti-cavalry spear unit, a heavy cavalry unit or two, a medium-light cavalry, a militia unit, etc. They also tended to try and make these units serve a distinct function. None of this is historical. I don't know how we would decide in the absence of much historical research what values these units should have in comparison with each other. Based on descriptions from historical texts? These tend to be rather general. How can these be the basis for a determination about whether a certain cavalry should have a 3 or 4 charge bonus? It all comes down to differing opinions about emphasis.

That said, I modded the game to even out the knight Templar's charge bonus. It's ridiculous to have it be any different from the other crusader knights.