Well I have a 70 draenei shaman who is pretty well gear and can put out some massive burst damage and even then his lightning bolts crit for 3-3.5k so image 5 of those. I guess how I see it is at 70 you will need gear to be decent and being limited to mostly pvp it's going to take awhile to collect a decent set. Also as a tauren anyone gets close and all you need to do is warstomp to get some distance or just to get off a cast.
Every combo has its advantages and disadvantages so it's hard to decide..

One question though.. you can dot without facing the person can't you? I guess thats a huge problem for a shaman if you have someone running in circles around you.