Then a rather odd thing happened. I had him on 30%, confident my instant would bring him down. I pop 4x em+ns+cl. And he GAINS health? xP The druid that got the secundary hits even got his hp reduced by 50%! I honestly don't know what went wrong there.
If you look very closely the druid performed an amazingly timed Rejuvenation, then NS+Healing touch on your first barrage, and then a Regrowth +Swiftmend just as you pop your big guns. by the looks of his gear that was probably in the region of around 4.6k on your first barrage where only your main crited (1.8k due to resilience or not much spelldamage) so that covered the first bit. Then his Regrowth + Swiftmend (consumes the Rejuvenation) would have healed for at least 4.6k assuming his Regrowth didn't crit heal and he has at least 1000+healing. Unfortunately by the looks of it again on your second barrage only your main crited :S which means you were incredibly unlucky and he got around 10k perfectly timed to hit just as your damage set in.

Hats of to the doodoo
How much spelldamage do you have cos particularly against that group you hit very softly :S That will certainly get better with better gear

as for other stuff i noticed help your healer out a little with a chain here and there. Atm ur gear will mean he'll be healing his ass off, and you need to make sure he has mana.

be 100% sure to go for the highest threat first that means hunter/warrior then Mage/ehn shammies.. I noticed you went a little nuts on some warlocks, which should one of the last dps on your list, unless you realise they ain't casting dots but bolts.. Bolts will likely mean he's Destro and will own you if you haven't got your totems up.

last but not least!! gz on 1600!!!

moving up is always a good sign ^^