Try to choose on this site http://www.ac-schnitzer.de/bmw-automobile/wheel-selector/. Why don't you go on 19" wheels, look better on your Zed. I have Ultraleggera HLT 8.5x19" rear & front. I'm about to order AC-Schnitzer Type VIII...Something that might interest you,Oz and BBs transfered their production in China. The price has remain the same but the quality not, in last few months they had a lot of reclamations.
I've stated a link on my FB profile if you want to check how Z4 looks like with Ultraleggera HLT 8.5x19"
http://www.facebook.com/photo.php?pid=392262&id=1627255072#!/photo.php?pid=3258658&op=1&o=global&view=global&subj=768852689&id=558328793