Factory supplied cars with 20" wheels defintely had beefier wheels bearings than 18" wheel cars, as i've just gone through this and was asked by the supplier whether i had 18 or 20" wheels.
Wouldn't surprise me if other components were also diferent
ETA : link here to allgerman parts, you can see first set of arms are for 20" wheels (not brakes!), the last set are "not for rim size 20" "
http://www.allgermanparts.co.uk/defa...m-571.html?p=4