beat it 2nd try on 25 man - Key for us was chain fear (had loads of warlocks) and focused dps, and everyone using all CC abilities at all times.
They can't be tanked btw, no normal threat table works.

Yet to try 10 man, but according to guildies 10 man is much harder than 25 due to the fact that 10 mans don't have all the abilities of a 25 man raid.