Level 20 Librarian. Maxed out Frenzy and had the Furious Start book equipped. Nothing else that mattered.
Character levels ranged from 18-21.
Some slight changes to the OP, seeing as how I think knights do better single target dps. I killed him a bit further than halfway down the right side.
1 berserker in the corner killing regular sheep. Boosted him once, don't think it mattered.
on the super sheep, I had a single unboosted ice mage with maxed Chill on him at all times, though not strictly necessary, as the speed debuff stacks and can last for a while after you take the ice mage away. However, I found this to be better than 3 on him for the first leg, as it allowed:
2 max boosted knights on him at all times (and 4 more waiting in the wings), with maxed Strength and all the attacks.
I only had 5 rangers, but 6 would work better if you have the Psych for it. One had maxed Deep Shot and Range Focus to keep the bleed debuff up. All others had Sharp Shooter, Range Focus, and Rapid Shot as high as possible. Oh, and I put them further back than the OP recommended. 4-5th rows, rather than 3-4. Less moving of them was required that way, and the healers can still be placed to give everyone the Inspire buff. However, near maxed Range Focus is required for this to work.
2 healers, with Zeal and maxed Inspire. Obviously boosted to max to get Zeal. Careful positioning will allow you to have all characters in range of Inspire.
The key to killing him as quickly as possible is to time your Frenzy to coincide with Inspire. Also, if you end up having extra Psych, don't forget that the healers will drop Zeal immediately upon getting access to it, so a good strategy is to do Frenzy right as one healer does Zeal, then unsummon him and drop and max another out right as the first Inspire wears off, maximizing time that Frenzy gets the Inspire help. Also, the Furious Start book works best when you drop knights in between uses of Frenzy, thus maximizing Frenzy time for them. Bonus points if you drop them right before a healer does Inspire, and you can use the above trick to ensure that. Pause game, drop knight, max boost him, then drop healer, max boost. And have some extra knights ready to go when the super sheep gets to the upper right. That's where he lost about 1/3 of his health in my playthrough, with 3-6 knights wacking on him.
My Psych was extremely stretched at times, but I only had one serious hick up, in the upper right "gauntlet" area. Trying to keep 6 max boosted knights on him was tough.
This isn't all necessary (other builds can kill him, if not quite as fast), but if, like me, you hate having to sit through a long fight, this seems to be the fastest way to down him. I haven't done the math, though, so berserkers might be better. I just went off the flavor text, namely that berserkers are primarily crowd killers while knights do better single target dps.