If you stick with the stock widths and offsets when going aftermarket, you shouldn't run into problems with Rubbing on H&R's. Dealing with the Chicago roads, that's going to be a totally different kettle of fish! Sticking with a 20" wouldn't be a bad idea in your area.
Most of the brands we carry give you the ability to customize the width/offset based upon your requirements in a 3 piece, some also in Monoblock.
HRE Wheels &
MORR are two excellent choices. Also, BBS is coming out with a 20" FI (Forged Individual) for the M5 soon, and will probably be one of the lightest options out there.
