I'm thinking a set of 16 x 7.5 Style 15 wheels from an E38 would take the car about as far as you could with the sleeper look. They've got the same look as the bottle caps that would've come on the car but instead of 14" wheels you'll be able to get a really fun performance tire on there. It's amazing how plain these look on the larger 7 series but look pretty amazing on the E30 in the link above that must have had a 5 bolt conversion.
At the end of the day though this is your car and you should set it up whatever way suits you, enjoy it!
