My set up im leveling is mageX2, lock, Druid(tank), Priest. which would be the same as you moving that lock to account 2.
Go destro on the lock and with the new patch everyone is happy with the new curse of elements! Locks are lot of dmg 8)
The shammy is a good team player too though :S I'd keep the priest but that falls back on personal preference. I would not switch out a mage for a lock however. Also keep your tank if you want to do instances for gear and whatnot.

Thats my 3 cents. Good luck with your decision!

P.s - If played right, the locks and mages would have KILLER finishers that go hand in hand with one another. I suggest fire spec the mages and possibly the lock 0/21/40 for some fun fire nuking, shadow destro still pumps out a lot of damage as well, but with scortches stacked high and curse of elements and sacraficing your imp- Your talking +30% to 40% more dmg, on-top of an already hard hitting class.

My other 2 cents. Adding up to 5! :X Going to have to break a dime here soon!