Do any of you use the Aqir Artifact for boss tanking? It is a very weird item. It's an avoidance piece, with an EH/mitigation use ability. The armor buff is not good for an aww shit button, IMO. Not like say the Moroes trinket or the Shadowmoon Insignia heal. Armor is good for shaving off small amounts that add up over time, not saving you from a killing blow.
So best way to use it, IMO, is to macro it to an ability so it's popped 20 sec. of every 2 min. This gives you a hefty 2500 armor when it's up, and an average of +417 armor through the course of a fight. But it's herky jerky EH. Only up 1/6 of the time. On average, the 417 armor is equal to about 27 Stamina in EH at 20K/20K hp/armor.
And the 1.9% static Parry is nothing to sneeze at. And any good MT knows that EH is not all that matters for hard hitting bosses. You want to keep up a minimum level of avoidance, too, to lower the chances that you will get strings of 3 or so hits in a row without avoiding one.
Anyway, I've gone back and forth on this. But I can't decide whether to equip the Aqir Artifact or Vengeance Card for hard hitting bosses like Archimonde. (My guild is still 5/5 Hyjal, 5/9 BT... we haven't done Sunwell yet.)
My current stats unbuffed...
w/ Vengeance Card
w/ Aqir Artifact
18,917 armor (+2,500 20 sec. of every 2 min)
Which would you wear against Archimonde? (Arch is the hardest hitting boss I tank currently.)
Ciderhelm's guide suggests at least 54,300 EH & 55% avoidance for pre-Illidan bosses. I'm way way way above the EH minimum, but only barely above the avoidance minimum.