In terms of combat capability I can see absolutely no benefit at all from having the personal belief slider at anything other than full barbarism.
Word is that party effecting skills are going to be charisma dependent.
Having the slider at barbarism doesn't just add to your str and con, it also subtracts from int and cha.
The chieftain is supposed to be a war leader/general role, however having this slider in either direction seems like it'd be either making your party buf effects sub-optimal, or making you personally a big wuss in terms of HP (damage I'm not so concerned about).
So far I'm thinking I'll probably try to have that slider more or less neutral and see what evolves. I'd kind of like to have it on the civilized side, however I'm not sure if I could deal with having 30% less HP than neutral or 60% less HP than a barbarian...
What does everyone else think? Note that this isn't a call for a dev change, I'm just curious as to how people perceive the way it currently is and how they plan to play with it.