I've tried Noth the plaguebringer, should be doable with 5, I just ran oom and didnt try again. Only trick is near the end, the adds start using lots of AoE, so they need to be stunned (pally tanks ftw) and killed quickly. Safety dance should be fine too, provided you can move well enough, as there is no enrage timer. Spider wing can probably be done too, the Adds will be a bit tough with one tank, but maybe some encounter specific macros will help. I think the only thing you COULDNT do without a second tank is Thaddius, and 4 horsemen. Everything else can be done if you are overgeared in heroic badge gear. Instructor Razuvious might be impossible as well, cause youd lose 1 dps to the MC... At least youll be able to bypass the bosses and go straight to Sapph, he's doable with 5, just a lot of AoE...