I have 6 boxed for over 6years now. Usually I fire up 5 accounts and use a cleric merc. But on raid events where you cant use them I use cleric and shmy for heals.
Shaman and monk are awesome combo but I think you are forgetting that you can easily add a merc cleric and you dont have to go T5 merc if the 97pp every 15min is the concern, you could easily go with a lower Tier merc and still have great heals on demand plus res's.
Pro's on bard;
Increase grp dps, duel wield plate class, Can tank,single pull across zone,
can highsun mobs (this sends a mob back to its spawn location and wipes aggro), increase grp mana/hp regen, slow/dot/snare/mez mobs,decent dps,
mez note: bards can only mez ONE target at a time so true cc aint gonna happen.
Pro's on ENC:
grp haste, mana regen , slows, Crowd control....
NOTE: my enc almost never dies as the enc mac I use starts mezzing mobs at a range of 80 so they get mezzed long before they can whack the enc
however DPS on enc... what dps? hehe
Something that I have found out from five boxing. you are never gonna have a true perfect grp so what i did is have the Enc/bard on same account. Depending on situation I pull out enc for CC and for grinds because i five box I useally use enc cause i just go tag 4 or 5 mobs with monk and dont bother wasting time single pulling. Sometime keep Time of how long it takes you each run out for a mob and back to camp. it adds up fast, whereas if you pull 4 or 5 at a time you actually kill way faster. As in over say 30 min or an hour you will have killed a lot more mobs by pulling 4 or 5 at a time
My favorite Dps grp is zerker,ranger(tank ;p),Bard,Rog,monk,Shmy
can you say SICK DPS
thankfully a LOT of people on this site have pm'ed me their strategy/bits of macs/holyshit/downshits so that I now rock the dps.
Other combo's I use for boxing older Raid events
Warrior,Ranger,Enc,Rog,Cleric
Mage,Shd,Mage,Rog,Cleric
Accounts look roughly like this
Warrior,zerker,mage
Ranger,Shd,Wiz*rarely use*
Enc,Bard,Mage
Rog
Monk,Cleric
My point is that since you are going with 3 accounts you could have both bard and enchanter, Then use whichever you need. For most days the bard would be fine but when you need true Crowd control whip out the enc.
Also you said you wanted a cleric so your shmy could dot? /boggle you need a way better mac. There is NO reason your shmy shouldnt be doting the hell out of the mob then healing as needed. Shmy dots do rock. there is a nice shmy mac on this site I think shmbot is name or something like that Havent used it but have seen it. I think JJ wrote it any who check that out or find one that will dot / heal.
all my toons are lvl 90 with over 3kAA and full T4 grp gear. Macros make earning exp/ lvls / aa fairly easy so don't be discouraged about thought of lvling a bard and enc on same account. I would start with bard as it sounds like you are only doing grp content so the extra dps/ tanking of bard would be a great addition for your 3 box.