perma, MM, like the fire giant belt... not bull's strength or empowered bulls. it should be difficult for a pure fighter to reach the +12 cap.
and I'm not talking pvp... which is impossible to balance in this game.
Actually I'd rather go the other way in the balancing process. For instance, a level 20 fighter has a BAB of 20 but how can he/she reach or even get close to the AB cap that a fully buffed cleric(divine favor/power) or COT(divine wrath) will easily reach? Items or multiclassing. Strong items can help a lot to balance classes which cannot buff themselves, like fighters and several other martial classes. A fighter without equipment is a dead fighter.
From a RPG standpoint, classes are fine, but in PvP the disparities are a bit scary, to the point where players will always pick the same few classes if no balance at all exists. Without reaching perfect balance, it is still possible to "attenuate" such disparities, as I have seen on a few PvP servers(maybe naming them would be seen as spamming?) in the past, yet it's indeed a difficult and lengthy process.