I always go function over style. For wheels I would go as light as possible and give myself at most a half pound for looks. So, find the lightest wheel(within budget) and anything within .5lbs heavier is allowed for better looks. With a grey car you can pretty much do anything you want for wheels. I would look into a funky blue accented wheel. That would look sharp on grey to add a splash of color, something that would complement the calipers.

bronze, at least I'm going bronze on my g82.