Stamina does not affect Shield Barrier. Only at Vengeance < 35,000 which is in no way dangerous.
Absorb is 2x AP (-AP from STR) or 2.5x STA.
28000 STA = 70,000 Absorb = 35,000 AP (-AP from STR)
You only need stamina to survive a period where you could not be healed and have to go through worst case. By default stamina on gear is already enough to do so (imo). Having more stamina allows for more EH but on the other hand costs more healing mana over the course of the fight.
Overdoing stamina does nothing for your absorb shield. Normal bosses will give you way more than 35,000 Vengeance.
Taking stamina is pointless imo. Going to hit/exp cap is not because you really need that damn rage to keep up the mitigation rotation.
Getting to 60rage / 6 second is pretty hard. Actually impossible without proc-luck.
In the long run Shield Block is on a 9second cooldown. Thus we would need 60 rage / 9 seconds. Which is possible to do.
spell rage cd rage/min
SS+SnB 25 - ?
SS 20 6 200
Revenge+proc 15 - ?
Revenge 15 9 105
Shout 20 60 20
Berserker Rage 10 30 20
Defensive Stance 1 3 20
Crit Block 10 3 ?
Charge 20 12 ?
We get 9 rage from Shout, Stance and Berserker Rage.
We get 30 rage from 1,5 SS.
We get 15 rage from 1 Revenge.
That is 54 rage. Getting the last 6 rage is up to Crit Block, Charge, Revenge or SnB proc.
Interesting. I need to adjust my spreadsheet since it is actually impossible to work on a 6second rotation later on. It has to be 9 seconds.
Actually getting sustained 60rage / 6sec is pretty much impossible. What really helps getting there would be mastery stacking and using Shield Block for critical blocks. But if you are on the Barrier side you would not do that.