I am anxiously awaiting the arrival of my Knights of Ruin (all 6 of them...thx ebay

) and have been debating how best to run them... are they viable at 2000 pts or a point sink ? Is Archaon needed to make the most of them ? Which battalion suits them ? 2 units of 3, a mob of 6, only 3...etc,etc.
Being a Daemon/ Mortals of Chaos player for years now I have lots of gifts from Papa Nurgle and creepy Uncle Tzeentch to aid my heralds of woe but am looking for ideas, and community input.
Automatically Appended Next Post: My first impulse is to run Archaon with them in order to Mark them (Nurgle) and help get the tally up and running ASAP. The knights bring the hitting power that the plague father's troops need and the Tally makes the Knights nearly untouchable to conventional attacks (ie less then rend -2, and non mortal wounds).