In 2v2 I've done Resto-Shaman and Resto-Druid and we hit 1650 the second week in s4 with quite sub-par gear.
Upside: Usually you eventuall win and you can beat almost every comp out there
Downside: Games are often over 20 - 30 minutes, and if you lose; well it REALLY sucks.


This was just in 2's I'm not sure how 5's would work, I'd imagine mana burn would be your bane.