Barbarian build question(s)

[MisterMorlock]

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[Mad Hamish]

... so, does 18+ CON unlock any feats or rage powers or somesuch? Every 4 levels I could get an extra hitpoint, but that's not worth it for me.

Well it does add 1 round of rage a day and +1 on fort saves.

But either you're confused about how hp work or I'm confused about what you write.

18 con doesn't give you an additional hp every 4 levels, it gives you 1 extra hitpoint per level over 17 con (equivalent to tougness).

19 con doesn't gain you a hp so you'd need to get to 20 con to get any more bonuses for pumping con which would take until 12th level. Which would get you 24 more hp than a 17 con would.

Whether that's worth it or you're better off pumping str is a separate question (I'd think that 1 point spent for 18 con could well be worth it but generally I'd be putting str up for a barbarian)