Religions for an ACKS game

Okay, so if you've been following my humble blog you've probably grokked that I'm interested in the Adventurer, Conqueror, King System by Autarch.  One of the projects they're working on for it is the Auran Empire campaign setting.  This setting is not the typical fantasy version of the European high middle ages but assumes an earlier era:

The Auran Imperial culture is based on Late Rome/Byzantine Empire. The Sunset Kingdoms of the west are akin to Indo-Persian civilization. The North is akin to German (Anglo Saxon) civilization. The Skysos riders of the far west are based on the Asiatic mounted hordes (Huns) that threatened the Late Roman Empire. Northern Elven culture is Celtic British, assuming it had not been Romanized.  The deceased classical elven civilization is “Atlantean” (hypothetical Bronze Age with both Greek and Egyptian motifs combined with early Christian burial practices). The deceased Thrassian (Lizard-man) civilization is inspired by Aztec civilization with an Assyrian aesthetic, while the deceased Zaharan civilization is inspired by Babylonian, Egyptian, and pre-Hellenistic Persian civilization.

But after reading these teaser bits on their web site I was feeling somewhat ambivalent about it.  On the one hand I like that I can go ahead and use all the cool stuff from Lore of the Gods d20 (Egyptian, Norse, Greek, and Mesopotamian deities and religion) by Bastion Press which I bought a while back.  Ever since I read the early D&D deity books I've wanted to toss these into my games.  But on the other hand when you use these deities in a European high middle ages type game it just doesn't always feel right.  (As an aside, the AD&D game run in college by my my friend George used the Greek pantheon and it worked okay.)  Plus, as a DM I feel like I'm being a bit of a slacker using existing stuff instead of coming up with my own creations.  But in the general time period of the ACKS setting these ancient pantheons are all good.  So if I run an ACKS game I will likely swap in the ancient pantheons which I've been studying for a long time.