I'm not going to go through theorycraft or anything like that, but I am personally not a huge fan of 240 armor. 15 agi nets 30 armor (some people forget that) but also 0.66% dodge with kings. 240 armor may be significantly better for trash mobs, but I'm guessing that someone would have a high threat set for trash mobs anyway.
As far as a boss fight is concerned, I would rather completely avoid a 10k cleave from Mag than mitigate a small portion of it. Or I'd rather dodge one of Prince's "triple-hits" in phase 2 than reduce all of his hits by 10 damage. To be honest, I like to take a little more damage for the mana return. While armor is far superior for sustained damage, for large amounts of spike damage mitigation can't compare to avoidance. Then again, as you can tell I've only MT up through T4 content so I may be completely mistaken on how the enchants scale later on.
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Gnome. It's what's for dinner.