I woke up this morning with a single thought in my head - hitting level 14 in ACKS might be somewhat sad, since you now can never ever gain any further personal power. I approve of the fact that power is capped, but having a hard "nope, you're done" solution is somewhat iffy. I propose an analogue to E6, but at 'cap level' for various classes - you stop gaining levels, and just gain a new proficiency every time you would gain a level. Might run into issues with low-capping demihuman classes, but overall it seems like it might be reasonable, especially if you start capping the number of times a single proficiency can be taken (I'm thinking Lay On Hands might be exploitable).
But overall, promising, and maybe useful for taking out those 30+ HD monsters. Not that it's going to be a concern for a looong time to come at the rate we're playing.