If you are going to pick up a BMW see if they can swing it for you. Their Fahrer training division runs the taxis do they not ? Better still book onto one of their ring driving courses, so far as I am aware they still use M3s. Also courses on the Grand Prix circuit.
http://www.m-power.com/_open/b/drive...ng.jsp?lang=en
The new years courses and venues normally appear in January - currently showing winter driving courses. May well be worth phoning.