Best parts of the AutoBahn?

Hello Euro F-chatters. At any rate, I'll be in Germany around the middle of January. I'll be in Munich and Berlin. At any rate, since I cannot bring any of my exotics so therefore I'll have to rent one.....grrrrr . I never got a chance to run all out on the autobahn. My questions are:

1) What part of Germany has the best, ungoverned stretches (Munich or Berlin)

2) Any good places to rent a nice F-car, Lambo, Porsche, Benz or Bimmer?>

 

Thanks for the info. I'm also willing to rent a seat in a F-Car for a ride.