Healing Gear Questions - Ulduar 25 Ready?

Stat Discussion
The following stats are of value to healing priests: stamina (almost meaningless), intellect (major), spirit (major for holy, medium for disc), haste (medium-to-major), crit (major), spellpower (major) and Mp5 (low). You can consider items with mp5 on them, but be aware that they tend to be less valuable than items with spirit on them.

Spirit
Regarding spirit specifically, assuming a typical amount of intellect (1400 raid-buffed), Disc priests can evaluate spirit at a ratio of ~ 2.75:1, or 11:4. That is, every point of spirit is worth ~ 0.36 Mp5 (factoring in Blessing of Kings and Enlightenment). That is really the only benefit you will see from Spirit, which leads to the conclusion that gemming for spirit as Disc is a silly idea.

Basically, though, if you see a cloth item (or a ring/neck/etc) in Ulduar, and you are concerned about its value for Disc, take the amount of spirit on it and multiply by 4/11 to get the equivalent amount of Mp5. It works out that 50 spirit = 18 Mp5, as a baseline.

For spirit and Holy priests, you gain no more regen from a single point of spirit (in fact, slightly less due to the extra 1% scaling in the Disc tree), but you gain a tremendous amount of spellpower. The ratio remains 11:4 for regen, but for every 11 points of spirit you gain, you also gain 2.75 spellpower. Note that "gain" here is used in the overall, after buffs, sense. So for a holy priest, if you have an item with 50 spirit vs an item with 18 Mp5, the 50 spirit gains you an extra 14 spellpower, a nice buff and enough reason to choose the item.

Haste
For haste, there are some nice cutoffs to reach. If you can hit 20% haste, it lowers the cast-time of a GHeal (without any procs/talents) to 2.08 seconds. If you never use GHeal, consider that it does the same thing for Prayer of Healing, and then you can stack Serendipity on top of that. For a Disc priest, you gain 6% from Enlightenment, and an additional 5% from Wrath of Air, plus 3% from ret/moonkin aura, leaving you with only 5% to gain from gear to reach the hard GCD cap on PW:S (given Borrowed Time). For a holy priest, you don't have Enlightenment, so you should consider picking up slightly more haste. I personally don't count Serendipity in any way, since it's mostly used for hasting PoH, and every bit of haste helps there. TL;DR:

Holy, run 12-14% haste.
Disc, run ~6% haste, or slightly under. To be honest, it's genuinely hard to avoid passing the 6% haste mark in Ulduar gear; you have to actively aim for all crit pieces, and even then picking up a T8 piece or two will put you there.

Of course, you can't always be sure you'll have moonkin/ret aura + Wrath of Air, so running slightly higher can make sense for those situations. It's certainly not expensive to get small amounts of haste.

Crit
Regarding crit, the sky really is the limit. There is very little reason to stop stacking crit at any level. You will gain 5% from talents (Holy Spec), and Disc can count roughly 7% more from Renewed Hope and Focused Will (since your tank should have Weakened Soul up almost all the time). Additionally, no 25-man raid would be complete without a moonkin in WotLK, so you can assume an additional 5% from that. Given that we will be running over 1400 intellect raid-buffed, that will grant us ~ 8.4% more, so there is no reason for any priest to be under 25% crit raid-buffed. In fact, once you finish your gearing (and pick up items which have crit on them), holy priests should break 30% crit, and Disc be closer to 40%.

Intellect
Intellect is incredibly valuable now. It converts to crit at a rate of 150:1 (with BoK) [for holy] and at a rate of 132:1 (with BoK+MS) [for Disc]. Additionally, almost all regen mechanics (external) are now based off percentages of your final mana, so the more you have, the better they work. Replenishment @ 25k mana is worth 312 Mp5, as compared to 190 Mp5 @ 15k. Your shadowfiend now restores mana based on a percentage of your overall mana bar, and Mana Tide totem continues its practice of doing the same. In addition, Hymn of Hope scales your maximum mana pool if it procs on you, which scales all other sources of incoming mana regen.

Rules of Thumb for Holy
Stack haste up to 12-14%. Think hard about whether you need more than that, given raid buffs and talents.
Pick up as much intellect as you can. It's always valuable.
Spellpower is always good.
11 spirit = 4 Mp5, ignoring spellpower gains entirely. Given spellpower gains, a 2:1 ratio is acceptable.

Crit is always valuable, although less so once you break 30% raid-buffed (diminishing returns on ilvl points spent).

Rough goals for the start of Ulduar 25 are to have 2800 spellpower, 26-28% crit, and 12% haste, along with ~500 Mp5 I5SR fully raid-buffed.

Rules of Thumb for Disc Healing
Pick up haste up to ~ 11% (hard-cap). Absolutely do not stack more.
Spellpower is always good, especially since you don't have Spiritual Guidance scaling your levels.
Pick up as much intellect as possible.
11 spirit = 4 Mp5, with no spellpower gains.

Rough goals for the start of Ulduar 25 are to have 2500 spellpower, 35% crit, and 8% haste, along with ~500 Mp5 I5SR fully raid-buffed.

---

Source