Frankly, couple of points to bring up.
First off, on Efflugent Earthsiege...valuable sure, but only in specific encounters ie spell damage ones.
If your boss tanking, Austere wins hands down,
If your trash tanking (melee) or need the extra defense then Eternal wins.
2nd point.
People keep talking about gem value and ignore DR.
What they dont seem to realize is that by the time your crit capped (540 defense) you are already experiencing diminishing returns.
The avoidance variance between the two gems (dodge/agi) is also subject to diminishing returns. This means that the more you stack avoidance, the closer the two get.
From a pure avoidance viewpoint, dodge is and will always remain better.
BUT the agi gem is also providing AC (not subject to diminishing returns) and melee crit.
For example:
Now, lets say you have 300 dodge rating and are at defense cap...you are getting about 6.44% dodge value from all that rating.
Now, lets say insteady you got 300 agi from gear, you will get:
Before kings: 4.94% dodge value, 600 armor and 5.76% increase to your melee crit
With kings: 5.49% dodge value, 660 armor and 6.34% increase to your melee crit.
Frankly, as tanks we would be much better off in some ways with Agi on our gear instead of dodge.
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Garath Lvl 80 Paladin, Gorefiend