Then you lose EH, DF, and Inspiration, not acceptable. As Lazare said, he's discussing the point in which you can cast holy Fire vs not and still gain healing by doing so. This is a haste issue, not hit.

First, all classes that can have Inspiration should have Inspiration, regardless of other raid members. The reason is that you don't have guaranteed 100% uptime just from one person having the talent-- you need crits to proc the effect, so having more people with the talent gives more stability. Additionally, sometimes, like on Nefarian or Wind Council, healers are spread out and you literally need 3 different healers each of whom have the talent. Sorry, Inspiration is a mandatory talent for raiding priests of either spec. Dropping Inspiration simply isn't a defensible position.

Second, losing Empowered Healing is in fact a huge deal. Greater Heal is Discipline's bread-and-butter tank healing spell (when damage is coming faster than Atonement can handle). Losing 15% of its throughput simply because you wanted to have 17% more hit on your Holy Fire is ludicrous, moreso because this choice also requires you to drop Inspiration.

The only spec I can imagine that can justify this is a spec where you ONLY expect to cast Holy Fire and Smite, along with a special DPS gear set for it. But you'd only use that for a gimmick fight anyway. And I don't think that's what you had in mind, since you suggested it as an option for people who didn't want to collect DPS gear.

I am only recommending a spec I know works pefectly since I and another priest use it weekly and we do not seem to have any problems killing the boss. But yes you are right, it is a gimmick spec for attonement-only fights. I definitely am not recommending it as a general raiding spec (but I kind of assumed that was obvious).

That kind of spec is viable for one fight only, Halfus. Any other fight you'll be a gimped healer for a marginal gain.

Recently, i was testing an Atonement spec, to see if it was even remotely viable as a DPS spec with a side of healing, becuase I was curious as to how far a Disc spec would go, in terms of DPS

WoW Talent Calculator - Sigrie was the spec I used (31/3/7). In order to test this out, I ran 100 3-minute tests with a comparable shadow spec (the one in my Armory).

Completely unbuffed, there wasn't actually that much difference: My Shadow spec was dealing 5.1k DPS with no buffs, while my Smite spec was dealing only 4.1k DPS. The major problem with the Discipline DPS spec was that it was running out of mana only 50-60 seconds in, whereas the typical Shadow DPS was slowly grinding down its mana. The rotation I used for Discipline DPS was thus: Holy Fire, Smite whilst the Glyph of HF was active, Penance, Shadow DoTs during empty GCDs. Another thing to note is my current trinket: World-Queller Focus. The trinket was used on Cooldown.

Given that Disc has very few instant-cast, damaging spells, I would not expect that Disc would be very good at all as a DPS spec in heavy movement fights/phases (such as Argaloth's Fel Firestorm).

Initial Conclusion:

As it stands, with the current mana raganeration levels, an Atonement spec is nowhere near viable for a long-term DPS raid-spec (>5 min. fight e.g. Theralion and Valiona). However, this is as things stand right now. Should things change on a larger scale beyond the next patch, then I'll re-investigate and update this thread accordingly.

I don't even do anything but smite and I could do much more than 4.1k DPS...it is also pretty mana efficient from a DPS standpoint...I have pretty high quality gear and have little mana problems when using just smite.

You should note that disc priests benefit alot from mana tide totems, next patch they're becoming raid-wide. And if shadow fiend & hymn of hope is combined you'll gain a huge deal of mana.

@ Halfus heroic 10 man (6 min encounter) I'm at 20ish% mana left when the combat is over. During that time I've got 2 mana tides, 1 hymn of hope & 2 shadow fiends. Wearing as much haste & crit gear as possible, but also hitcaped 17% from spirit with Twisted Faith.

for heroic halfius you'll be reforging spirit to output stats as a healer.

and taking twisted faith. Probably won't need that glyph, although a shadowfiend on CD, as well as smite glyph might help with overall dps issues. (I tend to raid heal twards the end as raid damage is higher than the tank damage, and we have smiters) (glyph of PS is also godly in that phase)

Please bear in mind that this is NOT with BiS gear. Plus I reforged my Mastery and Hit to Spirit (as Spirit gives marginally more hit rating with Twisted Faith) on my Non-Spirit carrying gear to reach the cap. I'm almost positive that, once I get into full T11, with all that Spirit, I can safely reforge my Mastery to Haste/Crit as and when needed.

It was something that I tested as an actual DPS spec, rather than Damage to Heal.

I've got Twisted Faith for Holy Fire hit cap, there's no other talent which is more usefull for smite/holy fire spamm.

This is pretty much how my halfus specc looks like: WoW Talent Calculator - Sigrie.
Main reason I've got talent points in PW:S is to shield up the whole raid before pull, and I also shield from time to time during fight to proc Borrowed Time & Rapture. Got both Inner Sanctum & Focused Will for reduced raid damage, the fire barrages hits for about 30k each, so it helps.

Since the fight is somewhat of a DPS race I try not to raidheal at all during the whole fight, unless the other healers can't handle it.

I have to strongly disagree with Twisted Faith on Halfus.

For one, I absolutely don't see how wasting a GCD on SWP or DP to be worth it over a Smite. On the similar note, even if Glyphed Holy Fire comes out to more damage and more total healing; I do not think it's worth interrupting the stream of incoming heals to the tank. -- That is, it doesn't matter if you manage to fit in 5 heals at 20% increased efficiency, your risk one GCD where the tank can get destroyed.

For two, any spec with Twisted Faith is giving up Inspiration. Who else is going to put it up, the Shaman? That's incredibly inefficient, not to mention a Priest can still swap and use Prayer of Healing sub-50%. Furious Roar is 100% physical, therefore Inspiration will mitigate the aoe damage by 10% (not to mention Divine Aegis is god-send in 10 man for this fight).

Also, it's worth noting, melee dps might be healed by Atonement, especially post-Furious Roar. Getting in 6 Smites is a potential of 6 people being healed, instead of 5 Smites and 1 Holy Fire resulting in those 5 people being healed for more, but the 6th person not being healed at all.