I have a team of 5 boomkins all geared around 710-720 ilevel with legendary rings. I can clear 4/8 mythic dungeons, misc bosses in the others, 7/8 heroics (I'm too lazy to try to beat the first boss in UBRS, lmao) -- I started doing heroics with this team with WAYYYY less gear, if you utilize some flasks, cooldowns, etc., you can get away with it all easily, especially if you get your toons some crafted pieces (weapon/darkmoon trinket/alchemy trinket if you like, was instant-OP for boomkins!).

Feel free to Battletag me if you ever log in: Phrygian#1161