Was playing on with the target dummies and an idea came into my head: Is the ‘new’ Hymn of Hope worth it if timed right?
This is entirely from a priest's perspective, and I'll be honest, I'm a biology major, so let me know if my math is screwy or my logic is broken somewhere.
Starting with Shadow:
We have 2 abilities which return mana based on % of total mana (not going to count replenishment here): Sfiend and Dispersion
Sfiend: 15s duration, 10 restores of 5% of your total mana
Dispersion: 6 restores of 6% of you total mana
For the sake of keeping DPS going, and to see, first we’ll assume HoH is cast for 1s just to get the 20% additional mana buff:
With 120% mana, each tick of Sfiend=6% of your normal mana
With 120% mana, each tick of Disp= 7.2% of your normal mana
Assuming you cast Sfiend right before using HoH, and blow dispersion right after the GCD resets, you get 8s worth of ‘ticks’ of each with the buff up, this means the full dispersion (6.5s should remain when dispersion is cast, leaving .5s to spare, I know this is cutting it close) and 8s of the Sfiend (it will be up before you get the buff and after you get the buff.
8s of dispersion at 7.2% regen=43.2% regen overall
8s of Sfiend at 6% regen per tick…(is a bit more complicated. Sfiend attacks every 1.5s so in 8s he gets off 5.333333, which we’ll round down to 5 and count that 1/3 chance of getting a sixth attack in as just a bonus)=5 attacks at 6% and 5 attacks at 5%=55% regen overall
So with Hymn of Hope’s 20% max mana increased buff up, and having sfiend up right before using it and going dispersion right after using it, you stand to gain 98.2% of your maximum mana.
Now for Replenishment: .25% of mana per second. Over that 8s with 120% max mana, you stand to gain .3% of mana per tick, or 2.4% max mana over 8 seconds
So by the time that sfiend dies, you will have gained 100.6% of your normal maximum mana…now to factor in the drawback.
HoH drops you out of shadowform yet, so you have to waste 1161 mana to get back into it at level 80. If you hadn’t of wasted time with HoH at all then during that Sfiend/dispersion/Replen sequence you would have gained: 50%+36%+2% mana back which is 88% overall.
Therefore, to ‘make’ extra mana via HoH, you need to have Sform cost less than 12.6% of your maximum mana, which means you need to have over roughly 9214 mana. If you have around 17000 mana (hopefully you have at least that or more) by using HoH you gain an additional 981 mana (15941 with HoH (and less Sform cost) vs. 14960 without).
Things I have not taken into account or blatantly ignored: Possible Imp Spirit Tap Procs, Any random spirit increasing trinkets/whatnot that you might have procced during this time, the possible 1 tick of HoH that gets off during the GCD before you can stop the channel via Dispersion, the boost to natural spirit regen. This means that you can easily get MORE mana back and make a bigger difference is some/all of these apply.
Continuing to ignore those things, you would need 193500 mana without the HoH buff to end this sequence with full mana (after having gone back to shadow form and not including other spells cast during the remaining 7s of sfiend after you're back in sform)
On the flip side, if you are Holy/Disc doing the same thing with HoH (casting it then just breaking the channel with a heal, or even letting it tick for a few if you are at a lull in heal duty), assuming Sfiend and Replen are ticking you stand to gain:
Sfiend: Same as shadow, 55% regen over 15s vs 50% regen
Replen: Same as shadow, 2.4% max mana vs 2%
So over that same period of regen, you’d gain 57.4% of your mana vs 52% of your mana, a gain no matter what. Again assuming 17000 mana, you get an additional 918 mana. (9758 with HoH vs 8840 without)
If Rapture (the Disc Talent) procs during those 8s, you’ll get 3% of your normal max mana back instead of 2.5%, meaning an additional 100 mana (at 20k mana, an easy number for Disco priests to achieve)
I would show how common healing trinkets like Spirit World Looking Glass On Use would also benefit during this time, but that math is likely beyond me Suffice to say it would make the difference even greater.
Let me know if there's faulty math here or if I should redo some thing differently. I know that I'm not taking into account Replenishment over the entire 15s that Sfiend is up, this is because it will inflate the numbers on both sides equally, and didn't seem necessary.