I thought I'd write a little post on one of my favourite tanking stats, agility. It's an odd stat to be a fan of, since no tanking gear really has any agility on it. However, we have a number of times where we have the option of using this stat, and knowing those options is worthwhile in itself. What also makes the stat so odd is that it is a "jack of all trades" stat. It gives a little bit of everything: avoidance, EH and threat. In this post, I'm going to discuss why and when you should consider deliberately gemming or enchanting for agility.
The value of agility is easy to compare: sort of. What we can do is show how equivalent it is to dodge rating and how equivalent it is to armor. First, for dodge rating, you get 1% dodge for every 39.35 dodge rating. For agility, you get 1% dodge for every 52.08 agility. However, in almost every raid context, we'll have Kings. So this means we really get 1% dodge for every 47.35 agility.
So, in terms of pure avoidance, 47.35 agility is worth 39.35 dodge. That means that 1 agility is worth 0.83 dodge rating, in terms of pure avoidance.
Dodge obviously wins here, but avoidance isn't the only thing that agility gives us. It also gives us 2 armor. I won't include Kings here, because that would be cheating. Why? Toughness gives us 10% more armor from our items. Kings gives us 10% more armor from our agility. It's tied. So, I'll consider the value of agility as equal to 2 armor.
So, purely from a survival perspective, agility is worth:
0.83 dodge rating + 2 armor
The question now is, how do I figure out how valuable these two are together relative to my other options? Unfortunately, there is no answer. Dodge increases avoidance and armor increases EH. We need different things for different fights, so the value of these two together can only be compared on a fight-to-fight basis.
However, what one can point out is that this actually implies that from an item budget perspective, agility is about equivalent to dodge+armor. In other words, if you're like me and dodge and armor are your two favourite tanking stats and you weigh them about equally, then agility is a reasonable option. How is this the case?
1 dodge rating and 14 armor cost the same in terms of item budget. So, that 2 armor is about 0.14 dodge rating in terms of item budget. Add them together, and:
0.83 dodge + 0.14 = 0.97
So, assuming that you weight armor and dodge equivalently in your item budget, agility is worth about 97% of either armor or dodge.
Now, you're probably reasonably thinking, "Yes, but 97% is worse than 100%, so didn't you just prove that agility is worse than the other two?". Yes and no. So far, I've only considered the survivability that agility gives. What I haven't considered is the threat. 52.08 agility also gives us 1% critical strike to our melee hits, which would mean 47.35 agility counting Kings. Compare this to Critical Strike rating which gives us 1% per 45.91. This includes our white damage, Hammer of the Righteous, Shield of Righteousness, Avenger's Shield and, I believe, Judgement. In fact, it affects everything that the Conviction talent affects with the exception of Exorcism. That's not quite all of our threat, since it doesn't include Seal of Corruption or Consecration, but it's certainly most of it.
Most of us would never consider gemming for Critical Strike. However, this doesn't mean we wouldn't sacrifice 3 dodge rating for 100 critical strike rating. So long as one gives any reasonable weight at all to critical strike rating, from a purely item budget perspective, agility is a huge bargain. It gives 0.83 dodge rating, 2 armor and 0.97 critical strike rating (not counting Exorcism).
Agility is therefore a great "well-rounded" stat, giving us a huge item-budget bargain. Where it would be most useful is in a piece of gear that is used in multiple sets. For example, let's say that you use the same leggings for your avoidance set and your EH set. Can't decide how to gem it? Try agility. It does a little bit of both and gives some extra threat to boot. It's especially nice for those red sockets. Either toss in a delicate scarlet ruby or a shifting twilight opal and get the best bargain for your item budget.
Don't forget some of the other sources of agility, too:
+22 agility to cloak.
+20 agility to gloves (people forget about this one).
+26 agility to weapon.
Mongoose to weapon (which gives a little more agility on average than +26 agility).
Agility is a great, well-rounded tanking stat, but it unfortunately isn't found on much of our gear. I hope I've done a good job of showing its utility and how it's one of the best item budget bargains around.