I'm running 15x7 Fuchs replicas with 205 60 on my 6 with standard fenders except that the edges are rolled. I had the wheels made with 135mm backspacing to make sure they would fit at the rear and ended up using 10mm spacers on the rear and 25mm at the front. So I think you will find that any wheel with 125mm backspacing or more will let you use a 7 inch wheel. For a list of 924-944 wheels see
http://www.connactivity.com/~kgross/944faq13.html