Well personally I am a player in the campaign not the DM. But I would have to say the deadliest encounter is well....,not to brag, none. We have the following characters in this group. And yes the DM does add more monsters to counter balance the number of players there are to keep it equal and fair.
But anyways we have : me a human cleric of kord 7 fighter 2 warpriest of kord 4. A straight human 13th level druid. A halfling arcane trickster 4 (I forgot what his other levels were). A human ranger 13(Abberation hater) A human warmage 10 Blood mage 3, A human vow of Poverty fighter 13,
a dragonborn bard 10 dragonsong lyrist 2, and a female human barbarian 14. So um yay, we kind got everything covered, especially healing, meat shields, trapfinding, and arcane knowledge. If they throw in psionics we are screwed however.
We killed the harbringer that was a cr 17 in 3 hits. One from a maximized searing light (me) a 35 point warmace smack (me again) and 36 points of quaterstaff damage from the vow of poverty fighter.