How much damage/DPS am I going to lose if I keep MB off cooldown for x seconds/for y% of the fight?
How much DPS am I going to gain from adding DP to a rotation?
If two priests A and B have VT uptime percentages tA and tB, how will their DPS differ because of that?
If I have to choose between two nukes, how much DPS will I gain from each choice?
An easy way to answer them all is with the concept of effective damage per cooldown, or eDPCD. This concept is not limited to Priests, I assume it can be applied to all casters (classes with filler+nuke mechanics). I haven't seen this way of looking at things anywhere, hence this post.
Before we get started I'd like to give a few definitions.
By filler I mean the spell with the highest DPET, but no cooldown. A nuke is a spell with a cooldown, and a higher DPET than the filler.
Now exactly how much DPS do we gain from using a nuke? There are two scenarios we have to look at: One where we only cast the filler, and another where we use the nuke on cooldown, and the filler while the nuke is cooling down. While casting the filler we deal DPET(filler).
In the second scenario we use the nuke on cooldown. Here's one way to look at it: While casting the nuke, we deal DPET(nuke), and in the remaining time we deal DPET(filler), so our average DPS is
But I'd like to look at it in another way. By casting the nuke we made a choice. We also could have cast the filler, but by replacing it with the nuke, we deal more damage. We gain damage from using the nuke over not using the nuke, but we can only do it once for ET(nuke) every CD(nuke). Our average DPS is
This motivates the definition of the effective damage per cooldown of our nuke,
Here's a DPS diagram for MB+MF to illustrate both points of view. Yellow means nuke, grey means filler. Note that the yellow shapes have the same area.
Now we can say: By keeping the nuke perfectly on cooldown, we gained eDPCD(nuke) over not using it at all. And we can easily answer the previous questions.
How much damage am I going to lose if I keep MB off cooldown for x seconds? Answer: x*eDPCD(MB).
How much DPS am I going to lose if I keep MB off cooldown for y% of the fight? Answer: y/100*eDPCD(MB).
How much DPS am I going to gain from adding DP to a rotation? Answer: At most eDPCD(DP).
If two priests A and B have VT uptime percentages tA and tB, how will their DPS differ because of that? Answer: (tA-tB)/100*eDPCD(VT).
If I have to choose between two nukes X and Y, how much DPS will I gain from each choice? Answer: eDPCD(X) and eDPCD(Y).
But enough with the algebra: What's the eDPCD for Shadow Priest nukes? The exact values of eDPCD of course depend on a lot of factors like gear, buffs, talents, trinket procs, partial resists, etc, so there's not one answer. What I can show you is the eDPCD for my own values, assuming zero latency. I happen to have very good gear as of 3.09, and after all modifiers I have on average 3072 spell power, 36.97% crit, and 28.77% haste.
My DPET(MF) is 3,927.38, and DPS(SW:P) is 605.70, so the base DPS is 4,533.07.
SW:D| 14.47| 0.32%
SW:D (4xT7)| 45.21 | 1.00%
SW:D (Glyph)| 54.04 | 1.19%
SW:D (both)| 87.86| 1.94%[/TABLE]
While the absolute values are highly dependent on the input, the relative values are probably pretty much the same for everyone.
What I found both interesting and disturbing is how small these values actually are in comparison to the base DPS. By using MB for example, the maximum gain is 5.2% of the base DPS if we somehow manage to keep it on cooldown all the time. If we manage to raise our MB uptime from 80% to 90%, all we get is is a measly 0.5%.
We can also use it to determine the expected value of the theoretical max. DPS by simply adding up all the eDPCD values. For me this means that even if I somehow manage to have perfect uptime on all the nukes (not possible in practice), the best I can possibly do is 5,958.16 DPS on average.