Back to the basic of this thread. If you are at 55 atm you can start in TBC and lvling will go so fast with the xp there. And you will porbably make it faster then when you lvled with 1 guy as you can do all the party quest and everything so much earlier then normal as of your sick dps as 5 el shammys, and soon you get 5x earth elementals and you should manage most 5mans easily So dont worry.. keep it going and you will find yourself at 70 for a long time for sure.

I started 2 weeks agoing with 3 new toons and they are 40 now.. and i thought the same as you... That aslong as i made it to 70 before expansion it would be fine.. but that wont be a proglem hehe