I'm sure someone much more knowledgeable than I am on this subject will be along shortly, but this may help you.
http://www.willtheyfit.com/index.php?width=225&aspect=40&diameter=18&wheelwidth=8.0&offset=45&width2=245&aspect2=35&diameter2=18&wheelwidth2=8.5&offset2=45
As to what they would look like, you'll only know once fitted, or finding a pic of them on a z4, or photoshopping them on.