Considering in Kings of War a Steam Tank is just a Elephant with a Balista I think you could not go wrong with Seleucids. They would probably have more unit options than Orc's anyway.
Apart from flying units and the Surge spell the fantasy part of Kings of war is not very fantastical, so Historical vs Fantasy is not such a big deal.
We ran Selucids vs Undead, and the Selucids curb stomped the undead horde in both play throughs. Their pikes were brutal. the non pike stuff was a bit more even, but with the pike block rules there was little hope for the ghouls/skeletons/other non sense.