If Zoro's main opponent in this arc is Killingham, as I suspect he is, then Killingham should at least be stronger overall than King and Lucci. Regardless, a Knight of God is the perfect target for Zoro to refine the efficiency of his conscious CoC Haki usage.
I'm curious how Killingham would fight Zoro beyond sending MMA or Sleeptids at him, since they shouldn't pose much of a challenge on their own. Maybe Killingham could absorb his spawned creations, similar to Moria's Shadows' Asgard technique (incidentally, "Asgard" comes from Norse mythology). Or, what if Killingham has a Hakuba-like state when he falls asleep? Perhaps he can manifest a stronger form of himself while sleeping.