I have a 97 528i with NO sport suspension and have the real oem M5 wheels and they do not rub at all. but if your car is lower (sport suspension package) or have modified suspension you will probably have to get your fenders rolled and possibly get the M5 fender liners. Remember they are 18x8 in front and 18x9.5 in the rear. there are some links in this site for fender rolling faq and m5 liner install.
(who needs some lowering springs that will not make my car too bumpy (i have a two year old). and possibly retain factory struts