Being an SCCA and IRCD (International Race Drivers Club) driver of a Formula Ford AND having driven the "fast" roads in the Netherlands, Belgium, Germany, France, Austria, Italy and Switzerland, AND having driven the Nurburgring in Germany, my husband agrees with Lee's comment.
If you want to go fast and have fun, with a few caveats, go to the Nurburgring and drive the Nordschleife -- http://www.nuerburgring.de/en/fans-info/race-tracks/nordschleife.html. You cannot drive a normal rental car there. In fact, the agencies supposedly check the parking lots to be sure their rental cars are not even parked there.
You can rent a specially prepared rental car to drive the Green Hell. My husband rented from Rent Race Car -- http://www.rentracecar.com/. If the link goes to a German page, click on the British flag. He went plenty fast and was happy with the 8 laps he did in a Suzuki Swift, but you can go with the higher end cars if you want. It just costs more money and you may not go any faster. There will be other cars and motorcycles, slow and fast, on the one-way road. It is NOT a boring drive like the autobahn.