What kicksome says is true, shammies ,might have mana issues at 85 with lower gear.
Once you get them geared up, mana becomes almost no issue, thunderstorm+shield do enough mana regen.
At first I was running oom during trashpacks, had to take a manabreak after each pull.
Now (ilvl 347-350 on the shammies) I can rush through a dungeon taking even multiple trash when the pull screws up
DPS is around 8-14k depending on the pull.