Our core was Roktazza (my warrior), Zinzin, and Karaka (rogue alt of one of the Bloodmoons). All of these were level 18, which is a bit lighter than I've been doing WC before.
We picked up a 21 druid and a 25 priest.
As we were clearing toward Cobrahn, Karaka went offline suddenly. (I found out this morning that his power had gone out.)
We waited for a few minues, then continued clearing to Cobrahn.
When we got to Cobrahn, we decided to wait a bit longer to see if Karaka came back, and went towards Pythas and Serpentis.
But Karaka never came back. So we killed Pythas and Serpentis as a foursome.
And killed Verdan (the big nature elemental).
And then we went back to Cobrahn (with all the respawn), and then killed Anacondra, and did the final event--all with just four of us.
Without any deaths in the whole run. I was impressed.
At this point, I'm feeling like a good tank, but not necessarily an awesome tank. Aggro kept leaking away from me and I'd have to scramble to regain it.
I wasn't keenly aware of the healing except during the Verdan and Mutanus fights. (Verdan hits really hard!) But, the healing must have been excellent, because of the whole no-dying thing. Yay for Zinzin, who seemed to be taking most of the healing burden. (And I didn't notice her being perpetually low on mana, the way she was when we ran Ragefire Chasm. Either the other priest was helping a lot, or we're doing something better.)
And the druid did a great job of being flexible. She would DPS on single fights, tank when we had two things to deal with (since we were low on crowd control), and I know that she was healing me some times.
I started the run about 40% through level 18. After the final event, I was 90% through level 19. After turning in all the quests, I was about 55% through level 20.
And, of course, when you're playing above average like this, the loot is a lot better for your level. I ended up with a mail breastplate dropped off Mutanus that I can't even wear until I'm level 23. And having blues that you can barely wear makes it a lot easier to get future such blue items.
One other thing that may have contributed to the run: over a few days beforehand, I had spent a bit of my blacksmithing profits shopping in the auction house, so I had a fair bit of gear that was as high-level as I could wear. (I replaced much of that during the run. I replaced my new belt twice during the evening.)