I'm at a very similar point in my progression to you, Hachoo. Level 69 5-man shammies.

I was in the Caverns of Time, did Durnhold with no real problems, so I went ahead and started the BM event cause I want that up front 8000 rep boost so I can get the crappy blue PvP gear right at 70. Made it through a couple of waves - barely - very chaotic and the melee guys really hurt. I just let Medvidh buy the farm since it was pretty clearly not going to be sustainable for 18 waves.

I'm going to try to recruit a tankadin to run with 4 of my five, who knows, maybe I'll find someone to run instances with. Got to get my second team with the pally leveling .....