Greetings Tom:
Last year the OZ Germany website recommended the 275 tire width on 17 X 10" Futuras for the rear of 500Es. I see they have now removed all of the specific 500E size recommendations from their website...ah, obsolescence.
Anyway, they don't rub at all, even with a full trunk. Guido has a lowered suspension, I believe, and that really changes things. I have not encountered a manufacturer that recommends the 10" rears with a lowered suspension. RENNTech told me they will only go to 9" rear rims on the W124 with their suspension package, although they offer 10" OZ-made rims for use at stock height.
I really need/use the GPS for speed measurement, both while travelling down south (we use KPH up here) and rallying. Accurate to .01 mph...awesome technology! The unit, remote antenna and custom installation cost me around $700US.