Author’s note: I have quit playing World of Warcraft before patch 3.0.5. Content in this article is unlikely to be relevant anymore and will not be updated.
Several of my blogging peers have spent time pondering or explaining the difference between stacking +MP5 versus +spell crit for healadins. While I refer you to the two links for specifics, I decided to compare both stats in terms of Item Budget.
What is the Item Budget? Well, most of us are familiar with the notion of iLevel – the level of any item in the game. What this iLevel number actually refers to is the sum of all various stats and modifiers you will find on the item, calculated according to a more or less complicated formula.
People who want to get the detailed research on the matter will find this wowwiki entry interesting, for the others, suffice to say that all stats and bonuses aren’t created equal in the formula – an item with iLevel 150 for instance would sport a massively higher number for Armor stat than, say, stamina. We will therefore compare the benefits of Crit vs MP5 in terms of how much of it you stack on your gear, all other things being equal.
We are playing with a fictional level 70 paladin sporting 10000 mana (wow, I want that), 5% base spell crit rate, 1400+ healing and 0MP5.
According to the above-mentioned wowwiki entry, each point of MP5 weighs 2.5 points of item budget. Each point of combat rating weighs 1 point of item budget.
You need 22.8 Spell Crit rating for 1% Crit chance. Therefore, 1% Crit chance = 9.12 MP5.
Time to OoM
The figure below shows how long your can keep casting with either stacking MP5 or +crit:
The blue line shows maximum casting duration, spamming Flash of Light 7, until you run out of mana while stacking +Spell Crit%. The red line shows the maximum casting duration under the same condition but spending the same item budget on MP5 instead.
This is of course in the nice theoretical situation where the healadin just stands there casting without interruption or lag.
The other figure of course is in terms of efficiency. The figure below will compare how much average healing each stat can provide during the casting duration:
The red line shows the total average healing ouput while spamming Flash of Light 7 until OoM while stacking MP5. The blue line does the same but with stacking +Crit % instead.
Where it gets more telling is with the green line: this one shows the healing ouput you have with stacking MP5 but limited to the maximum casting time of stacking +Crit %.
All things being equal, stacking +MP5 will let you heal for more over a longer time, whereas +crit will provide you with much more punch during a shorter timeframe.
In terms of bang for your bucks, our last figure shows where we stand stacking what:
In blue, how much extra casting time you get out of stacking MP5. In Red, the extra total healing you get out of this when compared to +crit budgetization, and in green, the loss of healing burst generated by MP5 instead of crit (that is, we measure the deficit in terms of healing done during the time you could cast if you were stacking +crit).
What does this tell us? MP5 allows you to keep casting longer but only for little more healing done than +crit. For PvP which is all about bursting, MP5 is pretty much useless, but for PvE, longevity definitely plays a role in raid content.
In terms of pure healing potency, +crit gives you more bang for your buck. So purely based on such theorycrafting charts (and let’s never forget that in practice constant, non-stop casting without a single overheal never happens), for PvE, stacking +crit should probably be given more weight on your kit than +MP5, but neglecting one in favour of the other will definitely prove a mistake.
For the other vital considerations tied to practical casting instead of funny number games, I kindly refer you back to Rohan and Zerei.