When does Gandalf actualy cast spells in LotR? And no, I don't mean in the movies.
forgive me, its been awhile since i picked up the books, and i couldn't stand the movies.
in the hobbit, when the dwarrow and bilbo get captured by goblins, he slaughters a whole room full with some kind of hocus pocus. one could suggest it was his fireworks, but the fact that only the goblins were charred kinda says otherwise.
in LotR, when aragorn, frodo, and the rest of the lolipop guild are on their way to elrond, i believe after frodo was stabbed but not sure, they look out and see a mass of lightning striking a hill. you later learn that was gandalf throwing down with the nazgul. My impression is both were flinging lightning bolts at eachother, but it you are looking for explicits "he cast "thors can of whoop-ass spell"", you won't find it, all you will find is the thread deterorating into a flame war.
there are others, but thats all i can remember in enough detail to mention.
just to be on topic, i like the idea, just not sure its hippus-ee. Yeah they are horse people, but they aren't really mage people, and that seems more like a mage thing then a horse thing, you know? not that it really works for the amurites either...