Just beat the Gladiator Arena finals, the third fight took me 23 turns. At least ten of those consisted of my Wizard chasing their Priest and Wizard around in circles because Gary's Priest couldn't reach me and his Wizard couldn't get most of his spells past my Resilient Hide armor. Meanwhile I was only doing a few points of damage at a time due to their armor. I'm starting to wonder if after a certain number of rounds the game should start awarding a victory point to each side for surviving so long just to put matches that are settling into a stalemate like that out of their misery.
Oh! You mean single player. I thought you were asking about PvP. While testing the AI just standing around and passing every turn I got up to 47 turns. I'd heal up, go do minor damage, duck back and do it again. Took forever.
I just finished that fight myself: my priest had lots of frenzy and Bad Medicine, his had Heavy Armor and Minor Heal.