I made a similar decision recently. Currently I'm running pally, shaman, shaman, mage, mage at lvl 62 and it's working fine for instances. I use focus for sheep targets on mages and most pulls are a breeze.

I put that team on hold and am leveling a warlock team, my plan is to sub one of the mages for a warlock in some instances where lock CC is better.

Personally, I wouldn't run with less than 2 shaman, the grounding and tremor totems are good enough that I want at least 2 of each.