I'm in the middle of a RAF at the moment, and while the teams aren't max level (2 teams @ 68 atm), I have decided that in the future (85-90), I want a 4x shammy and tank team to lfg with.
My multiclass team at 85 was slow to level from 80-85 due to the clickcastsequence loss.

RAF team 1 consisting of a bear, resto sham, and 3x ele shams was very enjoyable. Once the shammys got chain lightning, trash just doesn't stand a chance. Actually, the bear has a hard time keeping aggro on some pulls. The chain lightning x3 of team 1 also has the advantage of not needing to worry about mouse broadcasting the floor target, they just bounce around still stuff is dead. 4x healing stream totems keeps health topped up (don't need mana atm) and 4x fire eles is just lol worthy. (If only enh was a tank spec, I could make it 5)

RAF team 2 consists of a protadin, disc priest, ele sham, and 2 fire mages. Took the sham to gain the 5% haste and crit buffs for the mages, and kinda started regretting it. CL is still good it trash pulls, but the trash stays alive longer and the ele becomes in danger of ooming. I'd prefer a 3rd mage, giving me 3x scorches (no fly time, short cast 'finisher') and 3x blast waves. 2 make short work of low level trash, but 3 would be usable on larger pulls of tougher npcs. Thankfully I already have a fire mage at 85 that I can swap in when the time comes. Honestly haven't used the mage food or ports.

Planning to do a 3rd RAF team consisting of protadin, resto sham, and 3x ele shams.

My current opinion is that having the dps classes/specs the same means you're maximizing damage output in those areas that that spec works the best. Rather than having a jack-of-all-trades kind of deal going on. Having multiclass in my opinion just adds complexity for a minimal gain.

sidenote, I'm gifting levels in such a way I'll be able to try 3x spriest and 3x warlock at 85 by mixing in that original mixed class team. I'll have at least 3 of every caster class at 80 or above.