Critical strike is our haste because of Nature’s Grace

While Nature’s Grace and Haste Rating have similar affects on spell casting, it is important to note that they are not the same.

Haste Rating decreases your casting time and the global cooldown by a percentage. It affects all spells and all casts until the minimum global cooldown of 1 second is reached.

Nature’s Grace applies a 3 second buff that increases your haste by 20%. It has been confirmed that Nature’s Grace does in fact lower the Global Cooldown, but the GCD still cannot go below 1 second. Assuming full raid buffs a 1 second GCD is reached at 400 haste with Natures Grace. Since most raiding moonkin easily exceed 500 haste you can see that some of Nature’s Grace is wasted on short casts like Wrath, Moonfire, and Insect Swarm.

These differences are important for three reasons.

1. While most raidng moonkin still use Starfire as the primary nuke, it is undeniable that Wrath, Insect Swarm and Moonfire also play a big role. This means that Nature’s Grace will have a limited impact on 30% - 40% of Moonkin DPS.

2. When NG procs it is equivalent to 20% haste and reduces your Starfire cast from 3 seconds to 2.5 seconds (3/1.2 = 2.5). At level 80 It requires 656 Haste Rating to make the same reduction in casting time. One point of Crit rating will give you a 0.02178% chance to crit. Therefore, the Nature’s Grace component of one Crit Rating is equivalent to 0.1429 Haste Rating (656 * 0.0002179 = 0.1429). Even if you triple that value factor in multiple casts receiving the buff, it is easy to see that Haste has a much greater impact on Cast time then Crit does.

3. Finally, assuming a Lunar Rotation, Haste rating will increase your DPS more point for point then Crit rating will. The difference is a lot smaller then it used to be, but I expect this to remain true for all of WotLK. I have run the numbers for various levels of Crit and Haste Rating and Haste rating always increases DPS more for all reasonable levels of Crit and Haste.

Nature’s Grace is a very good talent, and significantly improves the value of Crit Rating when we evaluate stats. However by itself it is not a good reason to choose Crit over Haste. The Crit vs Haste debate really centers around Mana. Haste will increase your DPS more then Crit will, but it will cause you to run out of mana quicker. Therefore, the only logical reason to choose Crit over haste, given equal amounts of each stat, is because you have concerns about your mana pool and don’t think you can support that level of haste.