19" wheels really look best and is the more popular choice. I'd recommend that you check out the VMR V710 wheels. They feature a classic mesh design that looks good on just about any car you put them on!
Here are a couple pictures of the Hyper Silver finish installed on a Z4 which will give you a good idea on how this is going to look.
Last edited by ModBargains.com; 11-15-2012 at 08:35 AM.