Hi there, first time posting in these forums, but I'll give it a good shot, hopefully I don't repeat too much of what other people say and if I do, I guess that means what we are saying is probably correct and I'm glad I can help reinforce that.
Currently our guild is 2/6H and we are now progressing on Gara'jal.
Currently im gearing/gemming and enchanting for Spirit > 871haste soft cap > 50% mastery > crit
I'm gemming 320 spirit in blue sockets, 160spirit/80int in red sockets and 160spirit/160crit in blue sockets.
I'm also currently using Ancestral Swiftness for 4th row, and Primal Elementalist for 6th row for my talents.
I'm using Ancestral Swiftness because with this plus the haste buff from eleshams/spriests/boomys I can gain the extra tick on Riptide, Healing Rain and Earthliving without loosing too much mana regen from reforging to haste. Also, the instant cast can be very helpful, one specific time I can think of it being really effective is for Feng the Accursed on his Spirit of the Staff phase, I often find I need to use AS then HR for the Arcane Velocity channelled AoE ability, as the dbm timer can be really off so it can be very hard to precast with effective timing, with this you can put one down while running in, of course this can also be done with SWG, but If it's on the rotation when you are using healing cd's and not the barrier, the cast time can offen be to slow.
I'm using Primal Elementalist for one, because fire elemental does a decent amount of dps from only having to use 1gcd and two, because with both the earth and fire ele you can access It's ability called Empower, which if activated (must be activated manually, can macro this is) the elemental will channel this on you, increasing you healing done by 10% for the duration of the elemental (also increases damage done by 5% but this is not really relevant), this means you can have 10% increased healing for 2/5's of the fight, which is quite a decent amount especially on some of the harder bosses.
I'll now discuss my thoughts on the various haste caps, currently for most bosses, (most being them all apart from Gara'Jal because of the spirit buff) I find the 871 haste cap to be most effective, as I can gain a few increased ticks without loosing too much crit (I'll talk about crit next) and have the instant heal via the talent. Using EM/EotE and then getting the 2017 haste cap looks ok, but in my opinion, this is not as effective, this is due to the fact you have to loose 1.3k crit to gain this new cap, and this new cap only gains ticks on Riptide and Healing Rain and not for Earthliving, which the other cap+talent does have. Of course you are thinking EM or EotE will make up for this loss in crit/Earthliving tick, but to me EM is pretty useless, as shammy's already have 3 rather large raid cd's and these already combined with your other 2 healers cd's would make trying to fit in a time to use EM pretty difficult, EotE is nice, but I still feel the crit is much better for most of the current raid encounters (again Gara'Jal being the only exception).
Now just talking about haste in general, haste of course increases you hps, as you can pump out heals faster, but with current gear I feel the crit that would have to be lost to gain this haste would be too much, and the fact that the faster you cast spells, the faster you are going to get through your mana, and currently mana regen is THE biggest thing for rshammys.
Regarding Gara'Jal and haste, I feel like this is the one boss where it may be beneficial to go for the AS+3764 haste cap and then go with intellect and mastery, as you need ALOT of healing for this guy on heroic and if your gear is lower this may also help you alot on normal mode. Of course this is only viable because of the huge mana regen buff you gain when healing yourself in the spirit realm, and without the haste you will be continuously capping your mana while you have the buff. However, on heroic mode you gain a debuff after leaving the spirit realm, which prevents you from entering for another 30seconds, which means you can only go in every other spirit totem, and you will only be able to do this if you do not get the voodoo debuff, which means if you are not able to go into the spirit realm for say 3 rotations of the totem, you could very well be oom by this point as you will have alot less regen, and will be sucking up your mana alot faster with all that haste.
Now onto crit, for me, I have found crit to be THE best stat with current gear levels after spirit>871haste>50% mastery as the passive ability Resurgence got a huge buff with mop, meaning that the amount of mana your spells regen when they crit via this ability is quite large and I find it personally find it alot more useful than increased haste and mastery.
Quick regards to intellect, I feel it is currently NOT viable to gem for intellect or chant for intellect > spirit as the throughput gained from the intellect is far too minimal compared to that of the mana regen gained from spirit.
Mastery is a very easy stat to reach the cap now, as with the 3000mastery(at level 90) passive now provides 15% mastery, plus the base mastery of 24% as resto (a total of 39%) means you only need to gain another 11% (2200 rating) mastery for the cap, which is fantasic, and easy to get, and also this puts mastery at its most effective for the majority of fights (majority due to the fact mastery becomes less/more effective depending on the current health of the target, so if the fight has targets that are constantly at low health and taking large amounts of damage, one example being Gara'Jal, then mastery would gain increased effectiveness).
My stats. In my current gear with the raid haste buff (I shall only use this external buff as it is the only buff which effects caps) the mastery buff passive from shamans, Water Shield and Earthliving.
Spell Healing: 22,028
Haste: 7.01% 815 (I was on 895 which is the soft the cap, but the 80+ all stats chest enchant seems to have hotfixed an no longer gives a haste bonus.)
Mana Regen: 18,521
Combat Regen: 13,169
Crit Chance: 15.08% 4,886
Mastery: 50.04% 5208
I may add more when I read through this again, but I hope there is at least something that is helpful Also looking at it again it does look like a huge wall of text, but hopefully you can maintain interest and read through the whole thing ha.