If you already have a shammy at 65, use that.
I have 3 shaman specific keys. Totemstomp, water shield and flametongue weapon. Rest is on shared. Actually, water shield is shared with Inner Focus for my priests (it will add spellpower from level 71).

Edit: One has to simplify specs and make them revolve around multiboxing. For non-elites, dmg done is very biased as to the 1 char that get's the highest damage spell to land and do full damage.

I'd go with fire and scorchspamming for mages for nonelites and scorch*2 and fireballing for instances/elites.