I spoke about it in the Peanut gallery, but one my my NPC (sadly it wasn't one of my PC) made 5 critical out of 6 attack (1 critical per round for 5 round), but 3 of those critical was made on another NPC, so the players was mostly safe of that whirlwind of blow. Each making 2d6+19 damage.
I think no one have beaten that yet.