I think your kid is probably an Aspie (and a gifted one at that). That's good.
He's probably bored stiff at school, with his gifted brain stuck in a normal class. I know I would be. Not to mention freaked out by all the people and smells and crazy unpredictable events.
Transitions... insistence on order... Boy that sounds familiar. Making it easy on him by making life predictable (including the rules you have for him--write them down, make them completely dependable!) seems like the best way to go here. And making sure his brain has something interesting to work on rather than getting him into trouble all the time.
Teaching him to control himself is way better than getting anybody else to "handle" him. Such things are pointless and border on abuse half the time, what with people holding him down or drugging him up or any number of things to make him fit into their little perfectly organized classrooms.
Heck, bribe him to keep calm if you have to... it works. Punishment just isn't the way to help someone learn, take it from someone it was tried on!
There's no way he'll ever get over his tantrums if he doesn't learn it on his own. When I was that age I had tantrums like crazy; and the best way to let me calm down was to just stop interfering... I'd calm down on my own. Of course teachers want to interfere, which gets him even more riled up.
Can you home-school him? Sure it's more work, and you've got to make sure he has friends available... but keeping him away from clueless (and dumbed-down) school programs could be a plus, especially for the next few years.
Check this out:
Aspies for Freedom