After playing the older games and retro-games for nearly 30 years, I understand better how the XP charts of the various classes made them characters of as nearly equal power as you can be when combining magical ability and non-magical ability. It didn't make then the same LEVEL but rather gave the feel that the classes were of the same approximate power level at similar XP TOTALS. One thing difficult to quantify though is magic use. With the various effects that magic can produce, a true balance is an illusion (seriously, how do you compare a Fighting-man's combat ability to a Magic-user's spellcasting ability...apples and mangos).
After some experimenting with my PbP games and asking a friend that plays in another group to try it a few months ago, I modified the XP charts somewhat after getting their feedback:
|CHARACTER CLASS XP NEEDED TO LEVEL|
Clerics also includes Druids.
Fighting-men also includes Barbarians, Divine Champions, Rangers and Spellblades.
Magic-users also includes Illusionists.
* Denotes 'Name' Level - where a character with the class ability may found a stronghold. Characters' HD progressions also slow down at this level as well and XP needed is a flat amount. Most classes do not gain any new class abilities after this level.