Some say this is good option for inferno, but as far as i know this 20% comes after DR of your armor and ress, so it wont make any major changes. It's better to use IGNORE PAIN with 7 second rune. Becasue sometimes u just have to surive thru extremely high damage spikes areas and 7 second is just fine to kill 3-4 creeps from 10-12 sorrounding you. Threat shout won't make a big difference if Elite heavy hitting Molten, Fire chains, freeze gets you. Ignore Pain will let u srivve if you get cough by freeze in the middle of them pretty well.
I'm at the point of free farming A2 inferno.
You are using the most common build for Barbarian soloing inferno, so nithing wrong with it. You will prolly find it best till very very late game when you will have BiS items.