I'm just going to dump the rest of the research on BiS lists I had been doing before Nost shut down. All was untested for obvious reasons; not even having the appropriate content available to us except on the PTR for 1.9. So, take 1.9 and beyond lightly. It might be right, or not...
Patch 1.8 BiS Gear (9% spell hit)
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Lok'amir il Romathis
Tome of Arcane Domination
Mish'undare, Circlet of the Mind Flayer
Choker of the Fire Lord
Mantle of the Blackwing Cabal
Bloodvine Vest
Cloak of Consumption
Bracers of Arcane Accuracy
Bloodtinged Gloves
Firemaw's Clutch
Bloodvine Leggings
Bloodvine Boots
Ring of Spell Power
Ring of Spell Power
Neltharion's Tear
Briarwood Reed
Patch 1.9 BiS Gear (11%hit)
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Lok'amir il Romathis
Royal Scepter of Vek'lor
Mish'undare, Circlet of the Mind Flayer
Amulet of Vek'nilash
Mantle of the Blackwing Cabal
Bloodvine Vest
Cloak of the Devoured
Rockfury Bracers
Dark Storm Gauntlets
Eyestalk Waist Cord
Bloodvine Leggings
Bloodvine Boots
Ring of the Fallen God
Ritssyn's Ring of Chaos
Neltharion's Tear
Briarwood Reed
Patch 1.10 BiS Gear (11%hit)
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Lok'amir il Romathis
Royal Scepter of Vek'lor
Mish'undare, Circlet of the Mind Flayer
Amulet of Vek'nilash
Mantle of the Blackwing Cabal
Bloodvine Vest
Cloak of the Devoured
Rockfury Bracers
Dark Storm Gauntlets
Eyestalk Waist Cord
Bloodvine Leggings
Bloodvine Boots
Ring of the Fallen God
Ritssyn's Ring of Chaos
Neltharion's Tear
Briarwood Reed
Patch 1.11 BiS Gear (9%hit)
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Brimstone Staff
Mish'undare, Circlet of the Mind Flayer
Gem of Trapped Innocents
Rime Covered Mantle
Crystal Webbed Robe
Cloak of the Necropolis
Rockfury Bracers
Dark Storm Gauntlets
Eyestalk Waist Cord
Leggings of Polarity
Boots of Epiphany
Ring of the Fallen God
Band of the Inevitable
Neltharion's Tear
The Restrained Essence of Sapphiron
This was specifically tailored to guilds that actually could support a Boomkin (NOPE, Coalition, Grizzly, Ridin Dirty, and most likely Dreamstate). The thing with Boomkin is the higher the raid DPS, the faster the fight, the more likely it is for Boomkin to compete.
It has nothing to do with mana issues. Boomkin is strictly a burst class. Plain and simple.
Unfortunately, I don't think I'll be able to confirm any of this going forward on Elysium. I doubt I'll be raiding with Coalition (if we reform) and there honestly was no US guild (except Ridin Dirty) that was on par with the server power houses. Doesn't mean that there won't be one on Elysium, but that'd honestly be the best bet for me to continue the research on a higher level.
The strong guilds allow data and research to be done with a wide array of variety and quick results compared to guilds that take 3hr+ just to clear. Different mentality across the entire raid group. It's just that straight forward :\
It should be noted that even in the best situations and the best possible outcome for the Boomkin. Taking an equally geared Mage or Warlock will still be better. At least that's what I've worked out on paper, but it probably will hold true. However, if you're truly min-maxing like that the best setup is going to be 1 Shadow Priest and 9 Warlock's, so... ¯\_(ツ)_/¯