I've been raiding ToT on my disc priest for a while, and even if we got to 11/12, I'm ashamed to say that even now I'm not sure what stat to prioritize as disc. Opinions are pretty much mixed. Some said it's better to go full crit/mastery, some said it's best to keep a balance.
But what do you say? Should I veer more towards crit or mastery? Which stat would yield me a heftier hps boost? My role in a raid is prone to shift. Sometimes I'm on tank healing, other times on raid healing, and most of the times it's a mixture of both.
I try to keep my spirit around 8-9k, which feels right for me. Mastery works great with spirit shell. Crit works great with smite/holy fire. Figure out which one you use most and then focus a little more on stacking accordingly. I'd personally recommend mastery.
Have you tried going holy when asked to focus on raid healing?
Could you elaborate more on "how right" 8k spirit feels? Because for disc I never get a break. When I'm not using PoH/SS, I pew pew to get that attonement heals rolling.
Also, I can't really say what I use most. During a fight, I use a mixture of them except when encounter favor spirit shell or have damage boost ( jin'rokh's pools, horridon's damage increase debuff ), so I think it's kind of nice to keep them at similar levels since they boost each other.
I never thought about going holy, nor was I forced to do it. I have very little experience with that spec. What I can do as holy, I'll simply to better as disc.
A lot may have to do with your raid team as well. Assuming they're smart enough to move out of avoidable damage, are they popping personal survival cd's on damage spikes? Are your tanks using cooldowns when they get debuff stacks, etc? Do any of them have ways of replenishing mana for the group that they're possibly not using?
8k is a bit on the edge sometimes. I like to be closer to 9k. I use mindbender on cd and hymn of hope is used usually about mid-fight.
There's really no right or wrong spirit amount, it depends heavily on your playstyle, heavier pw:s usage or binding heal glyphed both requires a fair bit of extra regen to make use of. On fights where you can get away with atonement healing+an occasional pw:s on the tank you'll hardly ever need more than 10k, if you weave pw:s and binding heals to get through high damage periods you'll need way more. Just keep in mind that your amount of regen never has (or well, should have) an impact on the amount of cds (hf, penance, pw:s rapture, pom, cascade, etc) you cast, more regen only really means more (or lower hpm) "fillers", such as smite, PoH, binding heal, (non-rapture) pw:s, gheal. If this is worth it or not is up to you, I personally run with about 9k spirit and a dps trinket for most fights, but if I was progressionraiding on my priest I'd definitely regem/gear for at least 2-3k more on some fights (in particular the ones where I'd need to use the binding heal glyph, it's very awkward with my current spirit).
For 10 man the added damage is significant enough that you basically always should stack crit once you reach your desired spirit amount (having a balance of crit/mastery is very slightly superior for pure output). 1 int is still better for output than 2 crit at any realistical gear levels though, so try to get as close as possible to your desired spirit through reforging, reforge to crit secondarly, gem spirit if you were unable to reach your goal from reforging, otherwise gem int.
As Cookie mentions, you really want as much spirit as you are comfortable with. However, not only does this depend on your playstyle but also how good the group you run with is at avoiding damage and executing the required tactics cleanly and efficiently. The nature of those you heal with - both in terms of what cooldowns and mana regeneration possibilities are available - will also greatly impact how much spirit you want.
I personally use 12k spirit and on some fights even that is tight with high PW: Solace and efficient Shadow Fiend usage. I also couldn't get away with using two throughput (or a single DPS) trinket.
I wouldn't worry about the spirit issue. I raid 25 mans and while pushing heroics, I'm sitting at 15k spirit right now and OOM. But that's with heavy heavy PW:S usage and not as much atonement (Magaera is rough on the last few heads!). I use one throughput trinket and one regen. As your gear gets better you will end up getting more spirit, unless you take a ton of cloth with no spirit on it for extra secondary stats (which some people do!) If you end a fight with a lot of mana, start dropping spirit for crit or haste or even some mastery. If you OOM half way through a fight, pick up some more spirit or a better regen trinket. That's how you know how much spirit to run with
But I've been told that 10 mans is a crit or haste build since you tend to use atonement spells a lot. Plus the extra 45k dps is nice to get the boss down quicker, especially when your dps are still gearing up.
I'd go for int-focussed gemming with your gear. Int, int/spirit and int/crit or int/mastery and match socket bonuses.
Mastery or crit reforge doesn't really change anything. The difference is tiny. Crit is more dps and a bit more rng. Mastery is less dps but more reliable. There's an optimal ratio between the two but honestly it hardly matters.