I don't agree when it comes to discipline. The only reason a disc priest has so much worse HPS than a paladin is because of the mitigation we provide. If your greater heal crits and overheals the tank when he's at full hp, you should be pretty happy because you just gave the tank inspiration and a pretty substantial shield. If you also have a legendary mace (yeah I feel it's a waste to use Valanyr when I'm disc) you'll be pretty happy to use gheal just to pump the mitigation into the tank.

I honestly don't feel that flash heal does the job in 25-mans if you start comparing it to what a FoL or LHW does. Also the shield feels too small for it to be worth it.

We keep reading about all the disc priests here only using flash instead of gheal and at the same time boasting about how they never go oom and that they only gem int. I think you're gimping yourself with that mind set, when you can be going crit and haste for max mitigation instead (as tank healer).

If you want to be as well rounded as possible, spell power is by far the best stat to gem and go for. SP gives your shields the most bang for the buck, while crit is useless and int is overrated.

I feel as though the only way you are allowed to say you don't run out of mana, and are justified in doing so, is if every single raid member is alive at the end of the fight. I, too, have >30K mana raid buffed, and I frequently spend it. Yeah, I suppose there is some overhealing going on, but you might just be saving someone by casting a heal when you have time to.
Don't just stand there not casting anything. Be pre-shielding people. That's our job.
But, for the record, I don't think we should be doing all that much "healing" anyway. Our job is to focus on the mitigation, and I will frequently shield the raid if I have time while tank healing.

Because I'm a relatively new poster, I'll post my armory:
The World of Warcraft Armory

And a couple parses:
World of Logs - Real Time Raid Analysis

World of Logs - Real Time Raid Analysis

Have we decided that it IS worth it to break 4pc T8.5 when two T9 (lvl 245) are available?

Depends on your role and also on the fight at hand. How awesome PoM is depends on the fight at hand. I definitely would put a lot of thought into it for Heroic Twins.

The set bonus is important only if you are solely raid shielding. If you are tank healing it drops below 50% uptime and loses a lot of its value and on fights like IC that you have to time PW:S and not spam it on Weakened Soul removal it's even worse. It's impossible to get 125 raw Spell Power(assuming 50% uptime)from 5 pieces though the Int, Crit and the tiny Spirit increases make up for it.

Do you think the 2-piece set bonus (+20% PoM) is going to be a huge boost to holy healing? Right now PoM still constitutes a significant portion of my healing, so I know it's good for disc too, but I feel like its really going to be a boost for holy. Do you think it's relatively equal to the loss of 10% crit for PoH? Our holy priests top charts with PoH, even after the nerf, but I'm wondering if the T9 set bonus will make up for it when breaking the set.

The set bonus is very good regardless of your role. Parsing my own logs over many different encounters it is the equivalent of 151 spell power.

But I think people are also undervaluing the new set bonuses. I know we were all hoping that the 10% more to DA would bring it from 30% to 40%, but currently DA hovers around 20% of our total shields+heals, so 10% of that is 2% more healing, which is far from nothing (I feel bad for the holy priests, but the bonus is actually good for us). Similarly, if Prayer of Mending is even 5% of your total healing the 2-piece is a 1% bonus. Even if the 4-piece on our old gear was straight up 250 spell power that would only be a 4-5% bonus. The new set bonuses definitely seem like a downgrade, but not a massive one, so the increased stats will easily cover the difference and then some.

At the beginning, it is said "Metagems--- Primary choices... Selection based on whether you need more regen or more throughput.
[Insightful Earthsiege Diamond] - The highest regen meta available until extreme levels of Int. A 45-second ICD proc that restores 600 mana and 21 intellect."

This is the one I'm currently using... my question is, what is the definition of "extreme levels of Int"? And if you achieve this number, which is the recommended one to switch to?

Hey, moving aside from the tier bonus discussion. I was just wondering if anyone has any thoughts on the new trinkets, ie what would ur wishlist look like and why?

I believe the math said that over either 3000 or 6000 intellect, Ember Skyflare was better for regen. I don't remember the actual number, but it's definitely unobtainable right now. Once you have that much intellect, you are better off with Revitalizing Skyflare Diamond for extra throughput.

Thanks for the maths, even if they could maybe be more accurate according to the other posters here.

But I've been thinking about something that -as far as I know- has been missing in the GH/FH discussion : the extra 10% crit you get on tagets below 50%hp thanks to the 3/3 Improved FH talent. Did you include this data in your maths ? If not, a good starting point could be to assume that the healing target is indeed below 50%hp 40% of the time on hard hitting bosses (I think that they are the relevant encouters to compare GH and FH).
I would do the maths myself if only I knew how to do it