Regrowth

This is druids' quick, expensive heal.

In Cataclysm (as of 4.0.3a), all healers have the following types of heals:

Quick, expensive heal: 1.5 second cast, very high mana cost, high heal value.
Inexpensive heal: 3 second cast (usually talented to 2.5), very low mana cost, low heal value.
Slow, big heal: 3 second cast (usually talented to 2.5), high mana cost, very high heal value.

The mana costs differ very slightly between classes. Two of them have the quick heal cost more than the big heal.

Priest
Quick - Flash Heal
Cheap - [spell=2050]
Big - [spell=2060]

Shaman
Quick - Healing Surge
Cheap - [spell=331]
Big - [spell=77472]

Druid
Quick - Regrowth
Cheap - [spell=50464]
Big - [spell=5185]

Paladin
Quick - Flash of Light
Cheap - [spell=635]
Big - [spell=82326]

I'm going to be doing a more complete breakdown of the healing per mana and healing per second of Druid single-target large heals. For this consideration, I'm mostly looking at burst Hps (heals per second), so I'll be ignoring the HoT portion for calculations.

Regrowth Rank 12
29% of base mana 40 yd range
2 sec cast
Heals a friendly target for 2234 to 2494 and another 2345 over 21 sec.
Average Base Heal = (2234 + 2494)/2 = 2363
Base mana at lvl 80 for a druid: 3496
29% of that is 1014 mana, before reductions from talents.

Coefficient Approx 53.90% (64.68% with Empowered Rejuvenation)

Talents which effect HT:
Moonglow 9% cost reduction
Master Shapeshifter 4% increase healing (while in ToL form)
Gift of Nature 10% increase to all healing
Empowered Rejuvenation 20% increase to healing coefficient for Direct Heal and HoT portions.
Tree of Life 6% increased healing to everyone you can reach with your heals (45 yard range). Also, 20% further mana reduction
Improved Regrowth and Natural Perfection for 53% total crit chance increase and Nature's Splendor for a potential 0.5 cast time reduction.
Also, can be used with Nature's Swiftness for an instant cast.

Can't forget the Glyph of Regrowth +20% healing done for the Direct Heal and HoT portions if a Regrowth HoT is still on the target.

The case that I'll be looking at is maximum burst Hps. Specifically, I was contemplating a build that improves healing touch to be used as a backup after getting a Nature's Splendor proc from a Regrowth crit. Haste effects both spells evenly, so I'll be disregarding haste. Crits will play a big role because we're counting on Nature's Splendor for big bursts. I'll be doing several tables based on the druid's critical chance.

Talented Mana Cost:
Base: Moonglow: ToL: Both (multiplicative/additive)
1014 923 811 738 / 719
I'm pretty sure 738 is the value off my Druid on live with Moonglow 3/3 and in ToL form, so I'll be using that value.

Base healing (Without considering Crit)
+Healing Amount Healed HPM HPS
1500 4042 5.48 2021
1600 4120 5.58 2060
1700 4199 5.69 2099
1800 4277 5.80 2139
1900 4356 5.90 2178
2000 4434 6.01 2217
2100 4513 6.11 2256
2200 4591 6.22 2296


Considering crit, with a base crit chance of 10%/15%/20% and +50% from talent. HPS and HPM columns reflect a 60% crit chance
non-crit 60% 65% 70%
+Heal -Heal -crit -crit -crit HPM HPS
1500 4042 5255 5356 5457 5.48 2021
1600 4120 5357 5460 5563 5.58 2060
1700 4199 5458 5563 5668 5.69 2099
1800 4277 5560 5667 5774 5.80 2139
1900 4356 5662 5771 5880 5.90 2178
2000 4434 5764 5875 5986 6.01 2217
2100 4513 5866 5979 6092 6.11 2256
2200 4591 5968 6083 6198 6.22 2296


Note, all values are the average amount healed. Average amount calculated from:
(Base heal * non-crit chance) + (Base heal * crit chance * 1.5)
where 1.5 is the crit multiplier.

Now for a subsequent cast where the Glyph of Regrowth kicks in. Also, the cast time will be somewhat less because we just finished a Regrowth cast which may or may not crit. The heals per second (HPS) columns reflects a 60% crit chance on the previous cast (for an average cast time of 1.7s). The heals per mana column reflects the 60% crit chance for the current cast.

Average cast time derived from:
(base cast * non-crit chance) + ((base cast - 0.5) * crit chance)

non-crit 60% 65% 70%
+Heal -Heal -crit -crit -crit HPM HPS
1500 4850 6305 6427 6548 8.54 3709
1600 4944 6428 6551 6675 8.71 3781
1700 5039 6550 6676 6802 8.88 3853
1800 5133 6673 6801 6929 9.04 3925
1900 5227 6795 6926 7056 9.21 3997
2000 5321 6917 7050 7183 9.37 4069
2100 5415 7040 7175 7310 9.54 4141
2200 5509 7162 7300 7437 9.70 4213


That's a lot of spreadsheeting. For the time being, I'll leave my conclusion at this: 1800+ spell power unbuffed and you're looking at 4000 HPS (before accounting for your haste rating or Wrath of Air 5% spell haste!) from spamming regrowth at nearly 10 HPM. Buff food, a shaman totem and maybe an elixer, and regrowth spam is just plain retarded.

Eventually, I will make the comparison between plain regrowth spam and Regrowth - (Natures Splendor proc) 2.0 Sec HT cast - regrowth decisions. I have a hunch that the reduced crit chance on HT will kill the HPS consideration.

Edit: Good grief, I did all that work and now they're changing a key talent. (3.1 patch notes, taken from mmo-champ) I'll revise this shortly, when 3.1 has a known date.

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• Improved Regrowth (Tier 6) renamed Nature's Bounty. Increases the critical effect chance of your Regrowth and Nourish spells by 5/10/15/20/25%. (Previously increased just regrowth crit by 10/20/30/40/50%)
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It's a huuuuge mana hog but very nice healing spell to use in PvP because of its fast casting time (well, faster than Healing Touch).