You can check 5v5 arena ratings and filter by team comp, and check each battlegroup:
http://us.battle.net/wow/en/pvp/arena/bloodlust/5v5
Warlocks: zero teams of any rating.
Shaman (elemental or enhance): A lot of them, none over 1400, majority of games are losses.
DKs: A lot, none over 1500. Most or all under 50% win rate.
You can check EU realms as well if you want. There are a couple outliers but, honestly if you are coming back to multiboxing with the goal of glory in the dead 5v5 bracket, that time is probably over.
Actually, in general:
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