Allison Robert over at WoWInsider. com recently did an article on how to gear a balance druid (Link). It's a good article that comes at the topic from a different angle then I did and I'm sure some people will find it more helpful then my gear guide. (I'm not just saying that because she linked by blog for a 3rd time. Woot!!!!)
I want to assure you that the ranty nature of this post is not directed at Allison in anyway. She has done a great job of covering moonkin recently and her job is definately harder and her posts are more closely scrutinized then mine. As a result she has to make some concessions to try and prevent backlash, but there is one comment in her post that sent me a little over the edge.
When talking about gems for the head slot she said:
Meta: [Chaotic Skyflare Diamond]. Some prefer the [Ember Skyflare Diamond], however.
Sure, some people say that the Ember Diamond is better, but they are wrong.
Wrong Wrong Wrong!
Wrong Wrong Wrong Wrong Wrong! I can't say they are wrong enough.
What Allison's post should have said was:
Meta: [Chaotic Skyflare Diamond]. Period!! End of Discussion!!!
Here is why.
In terms of DPS:
First off, I want to say I can understand some of the confusion. If we sat down and wrote a moonkin rule book one of them would surely be Spell Power > Crit Rating, and anyone that knows basic math knows that 25 > 21. So I can understand the confusion if someone only looked at the gems very quickly. The [Chaotic Skyflare Diamond] is a bit of an exception to the rule. However, if you focus on the 21 crit rating then your looking at the wrong part of the gem. It is the 3% Increased Critical Damage that makes this gem so valuable.
First lets look at what that 3% Increased Critical Damage really means. It's not as easy as you may think.
Your spells non-critical hits always hits the mob for 100% damage. Critical hits then increase the spells damage by 50% for a total of 150% without modifiers like talents or the meta gem. The meta gem increases the total damage of your critical strikes by 3%. So without any talent modifiers, the meta gem will cause your critical hits to hit for 154.5% (150 * 1.03 = 154.5) of your normal strikes. Then Vengeance increases the bonus portion of your Critical strike damage by 100%. The extra damage from the meta gem is concidered part of the bonus damage of the critical strike. So, with Vengeance and the meta gem your critical strikes will hit for 209% (54.5 * 2 + 100 = 209) of your normal damage.
So you may be asking how significant is this extra damage. In short, it's huge. Lets look at some numbers.
1. I'm going to use a fairly average moonkin. I would consider this person to be partially geared or fairly entry level. For my calculations I am using a moonkin with just 2000 Spell Power, 35% crit (38% for SF with Imp IS), and 17% haste fully raid buffed. I will aso assume that he his hit capped.
2. I am also going to assume that he uses this build. It is a fairly high level raiding build, but I don't think there are any reasonable changes that could significantly affect my results.
3. I'm only going to detail the math on Starfire since it is our primary spell but I have run the math on Wrath also, and will provide the results below.
4. I assume that Moonfire and Insect Swarm are on the boss when calculating the damage for Wrath and Starfire to take full advantage of Improved Insect Swarm.
So lets look lets look at the average damage of a normal Starfire spell cast.
SF Damage = ((((1120 + (SP * 1.2)) * 1.17) * 2) * Crit Rate) + (((1120 + (SP * 1.2)) * 1.17) * (1 - Crit Rate))With the Chaotic Skyflare Diamond the average damage of Starfire is:
SF Damage = ((((1120 + (2000 * 1.2)) * 1.17) * 2) * 0.38) + (((1120 + (2000 * 1.2)) * 1.17) * (1 - 0.38))
SF Damage = (8236.80 * 0.38) + (4118.40 * (1 - 0.38)) = 5683.392
SF Damage = ((((1120 + (SP * 1.2)) * 1.17) * 2.09) * Crit Rate) + (((1120 + (SP * 1.2)) * 1.17) * (1 - Crit Rate))
SF Damage = ((((1120 + (2000 * 1.2)) * 1.17) * 2.09) * 0.38) + (((1120 + (2000 * 1.2)) * 1.17) * (1 - 0.38))
SF Damage = (8607.456 * 0.38) + (4118.40 * (1 - 0.38)) = 5824.2413
So as you can see the Chaotic Skyflare Diamond increased the average damage of Starfire under these circumstances by 140.8493. Now, we all know that 1 spell power does not equal 1 damage. So, we need to find out how much damage 1 point of Spell Power provides. We can find that with the following equation.
Damage from SP = (((1 * 1.2) * 1.17) * (1 + Crit Rate)
Damage from SP = (((1 * 1.2) * 1.17) * (1 + 0.38) = 1.9375
Since 1 Spell Power is equivalent to 1.9375 damage and the extra crit damage increased the average Starfire Damage by 140.8493, then the extra crit damage is equivalent to 72.6957 Spell Power for Starfire (140.8493 / 1.9375 = 72.6957). I have also run the numbers for Wrath and the results are a little bit lower. For Wrath the extra crit damage is equivalent to 65.5716 Spell Power.
It is also important to remember that not all of our damage can crit, but after looking at WWS reports I find that leaste 80% of it can on average. So I think it is safe to say for the middle of the road moonkin that I have presented the extra crit from the Chaotic Skyflare Diamond is equivalent to 55.3068 Spell Power ( (((72.6957 + 65.5716) / 2) * 0.8) ).
The Ember Skyflare Diamond on the other hand has a static 25 Spell Power and an extra 2% Intellegence. The extra Intellegence will give you a little extra Spell Power and Crit Chance, but even for a well geared moonkin like me it is only and extra 3 spell Power and 7 Crit rating.
Simply put, I have run this comparison for several different gear levels. The only way I could make the Ember Skyflare Diamond equivalent to the Chaotic Skyflare Diamond in terms of damage was to use rediculously low stats of around 1300 Spell Power, 20% Crit and 11% haste.
In Terms of Mana:
The only real argument that the Ember Skyflare Diamaond has is mana. In fact, I will conceed that it is better in terms of mana returned, but the difference really isn't that big.
Lets take the hypothetical moonkin I used above and assume that he has 1000 intellegence fully raid buffed. This means the Ember Skyflare Diamond will give him an extra 20 Int. The most obvious impact is that this will increase Mp5 by 2 due to Dreamstate. It also increases your mana pool by 300 mana, which increases the amount of mana returned from Moonkin Form.
Note: I am going to ignore Replenishment for now because it is impossible to figure out what the impact of that will be. In fact, it could be negative because the extra Int may cause someone else to get Replenishment instead of you.
The extra 300 mana means that every time you crit you get an extra 6 mana back with a crit chance of 38% for SF this means you will get an average of 2.28 mana back per SF cast. The average cast time of SF for the hypothetical moonking is 2.4017 seconds ((3-(0.5*0.38))/(1+ 0.17) = 2.4017). This means the extra 300 mana is equivalent to 4.7466 Mp5 (2.28 * (5/2.4017) = 4.7466).
When you combine this with Dreamstate the Ember Skyflare Diamond is equivalent to 6.7466 Mp5. However, this isn't a pure advantage over the Chaotic Skyflare Diamond because the 21 Crit rating on it has some mana affects also.
The hypothetical moonkin with 1000 Int will have a mana pool of at leaste 17000. This means that every time he crits 340 mana is returned. The 21 Crit rating from the Chaotic Skyflare Diamond increases his Crit Chance by 0.4575%. This means that on average each spell cast will return 1.5555 mana more then without the Chaotic Skyflare Diamond (340 * 0.004575 = 1.5555). This is equivalent to 3.2384 Mp5 (1.5555* (5/2.4017) = 3.2384).
Now, we can clearly see that the Ember Skyflare Diamond does have an Mp5 advantage over the Chaotic Skyflare Diamond, but the difference is very small. Again I have run the numbers for several levels of gear, and the Ember Diamonds advantage is between 3 and 4 Mp5 for all realistic gear levels.
In terms of damage, the Chaotic Skyflare Diamond is clearly superior. For the middle of the road moonkin I've presented it provides more then twice the damage of the Ember Skyflare Diamond. On top of that it is significantly better for a well geared moonkin and will only improve more as we progress into Tier 8 and Tier 9 content.
In terms of mana the Ember Skyflare Diamond is Superior, but the advantage is small and will not help anyone with serious mana issues. Realisticly Mp5 is not a good stat for moonkin. A majority of raiding moonkin don't have big issues, and if they did they could get more Mp5 by resocketing normal gems or by changing their talents around a little bit. Simply put, the 3 - 4 Mp5 that the Ember Diamond provides is not worth the 30+ spell power loss.
Addition: There are other meta gems available then what I have listed. However, none of them are great for raiding. If you would like to look at them you can find a list here. Most are PvP focused and I wouldn't recommend any of them over the Chaotic Skyflare Diamond.