Show me a real world case of someone wheels breaking due to powdercoat, not a friend of a friend who knew someone. If you can, chances are there was a structural defect in the wheel all along. 400 degrees for a. Hour isn't going t weaken the wheel. I've got a couple thousand track miles on my powdercoated wheels on the z and had a similar amount on the powdercoated wheels on the c6.
How a out metallic black wheels? black from a distance, but really sharp in the sun and up close. When I did powdercoat wheels, it was a very popular color with my corvette people. I don't coat them now just because they take too much time and I have a constant backlog of caliper orders.
http://img11.imageshack.us/i/dsc04949k.jpg/