I'm working up a Dwarven Barbarian THF build for myself, and I had two questions for those that have run barbarians.

1) How essential is the DR Boost enhancement? I understand what it does, but is its usage critical? And can you activate it while raged? Trying to allocate how I would like my APs and deciding between maxing the DR boost vs taking power rage 4 and axe attack 2.

2) With Extend Rage IV, how many Extra Rages are needed, on average? I was figuring 1, but have seen other builds say 2. Mainly looking for experienced input to help me make the final decision.