The main thing I have heard regarding shaman as DPS was mana issues though if you have a mage or mages giving free water then maybe it isn't as big an issue. Initial grinding via shaman DPS with no water on a new server may be a gold sync for awhile. In addition to spending more time drinking there may be some fights that are just not complete-able due to going OOM (not sure).
I don't know anyone who has done 4Shaman+Warrior but I believe Pertrolisk and some others have done 5 Shaman to cap and maybe they will chime in with some thoughts.
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