The two main gems I'm going to focus on here are:
http://www.wowhead.com/?item=41380 (32 stam, +2% armor)
http://www.wowhead.com/?item=41396 (21 def, +5% BV)
I realize that other viable options exist, including the 2% spell mitigation one. But for a majority of encounters, tanks are going to choose one of the two gems listed above.
The question then becomes which one is better.
The obvious answer is that 5% BV is better for faster, weaker hitting mobs and that 2% armor is better for slower, harder hitting mobs. This answer is such an gross generalization that for anyone with any interest in max/min and theorycrafting, it's unacceptable.
The debate between 32 stam and 21 defense is a different battle and isn't specific to these meta gems. For the sake of my comparison here, I will assume that 21 defense and 32 stam are equal. The point can be debated, but in that case all gems and enchants are brought into discussion. The real point of conflict with our meta gems is +2% armor vs +5% BV.
On 2% armor.
The amount of mitigation gained from a total amount of armor ("X"), against a (level 83) raid boss can be found by the following equation:
%mitigation = X / (X + 16635)
For example, if you have 22k armor, you will mitigate (22000 / (22000 + 16635)) or 56.9% against a raid boss.
To then figure out how much actual damage you take you have to account for how hard the boss is hitting. The harder the boss hits, the more damage 56.9% of his hit is equal to.
Therefore:
Total Damage Taken = Base Damage * (1 - %mitigation)
To find out how much you mitigate with an additional 2% armor we can simply use the following equation:
%NEWmitigation = (1.02 * X) / ((1.02 * X) + 16635)
The amount of damage that results in is:
Total NEW Damage Taken = Base Damage * (1 - %NEWmitigation)
Therefore, the amount of additional damage reduced by 2% additional armor is equal to:
Total Damage Taken - Total NEW Damage Taken.
On 5% BV.
The amount of damage reduced by Block Value is a very simple calculation. It doesn't scale at all with how hard you're being hit, making it much better against light hitting mobs, and worse against hard hitting mobs.
The amount of damage mitigated by BV is equal to BV.
The amount of additional damage mitigated +5% BV is equal to:
0.05 * BV
Conclusions.
Before I get into specific examples, the amount of mitigation gained from 5% BV compared to 2% armor takes into account three variables: Current Armor, Current BV, Average Boss Hit Damage. It is also important to remember that you are only guaranteed to mitigated damage equal to your BV when you're at "uncrushable" or 102.4% avoidance + block chance. Therefore, the equations and calculations I've laid out for comparing these two meta gems are only relevant when you will block every unavoided attack. If you're not in that situation, the value of 5% BV diminishes drastically. In addition, I didn't take into acount the threat and DPS gained by 5% BV. At current gear levels, maintaining threat is a non issue so it's not something to worry about. DPS is a valid point to discuss, but it's not within the scope of my comparison.
Examples.
"Low Level Set"
Armor: 20k
BV: 800
Average Boss Hit (unmitigated): 8000
Damage Reduction gained by:
2% armor: 39.23
5% BV: 40
"Low-Mid"
Armor: 22k
BV: 875
Average Boss Hit (unmitigated): 10000
Damage Reduction gained by:
2% armor: 48.48
5% BV: 43.75
"Mid Level"
Armor: 23k
BV: 900
Average Boss Hit (unmitigated): 12000
Damage Reduction gained by:
2% armor: 57.35
5% BV: 45
"High Level"
Armor: 25k
BV: 1000
Average Boss Hit (unmitigated): 18000
Damage Reduction gained by:
2% armor: 85
5% BV: 50
Note.
These are all samples of arbitrary stats. I wrote a small web app to calculate the benefits of the two meta given current BV, armor, and unmitigated boss hit amount, but I have no where to upload them.
Comments?
Jasari
Fri Dec 05, 2008 9:58 am
