I dont have my Durgeon anymore...but when I did have him, he was still a juvenile and was housed with a (quoted from above): 4" Clown Trigger, 8" Blue Throat Trigger, 8" Passer Angel, 8" Sailfin, 15" Volitan Lion, 30" Hawaiian Dragon Moray and a 30" Whitemouth Moray.
Those are all pretty aggressive fish (minus the Blue Throat). He was a slight pushover, but wouldnt take too much from anyone. No doubt that when he got bigger, he'd be something to contend with.
A friend of mine, who owns a LFS in Chicago, had a 10" Durgeon in a tank with a Japanese Dragon, 10" Naso and some other large fish. The Durgeon killed quite a few fish, that temporarily resided in that tank.