My std rims ( 3 spoke ally) measure 6+inch ish on the outside width. The magnesium marchesinis measure more than 1/2 inch more. In fact they are not far off 7 inches in total external width. Can't be bothered to measure too accuratley but will if anyone wants the exact figures.
Stimpy - that's what I mean about the measurements - your 3 spoke brembos would officially be 5.5" and the mags would be 6" - in all probability. That's from the internal diameter measurement (id).