I got all excited after a handful of attempts getting the third drake down with both me and my pet alive (affliction lock) only to realize the rest of the fight was impossible. Always thought the portal mobs were killed just to take away those dangerous debuffs. I guess ill find someone to duo it.
I found it easiest by far to just take two people and just do it the 'intended way' (not that 2-manning it was ever intended, but you all know what I mean). One person (me, on my DK) tanks everything as it appears, the other person (DPS monk) kills stuff and takes portals to deal with those adds. Neither of us were well geared on those alts at the time (Dread wastes quest gear, basically), and at no point were we ever in danger of losing. We figured it made more sense to just control the fight and handle it normally than to pray we had the DPS for a zerg kill.
But to the original question, it's something in the 100-150k DPS range. Not sure where exactly. Should be easy enough with two good (and sturdy) DPS; or a *really* hard push for a solo.