I have rented a few cars in Germany over the years. My first piece of advice would be to make multiple bookings with different rental car companies. Several times I have booked a particular class and ended up with the most boring or slowest car in the class. Status doesn't even help. Booked a vehicle at Europacar as Prem Exec. and was given a BMW 520D. Went across to Avis and walked out with a Audi Q5 S line, and it was a 30% cheaper. I now ask the counter person what they have, smile nicely, and generally get something I want to drive.
Once outside the Berlin Ring Road it is quick drive south - plenty of places to hit the speed limiter (generally 250kmh). In the right vehicle you can get to Dresden in just over an hour. Some nice winding roads in the hills north of Dresden and south towards the border (but have speed limits :-(). Make sure you visit the VW factory in Dresden (
Transparent Factory - Wikipedia, the free encyclopedia). Halfway between Dresden and Leipzig is Colditz - great place to visit - WWII POW camp and now a hostel and museum (
Colditz Castle - Wikipedia, the free encyclopedia)
Also note you can't take German manufactured cars into Eastern Europe - you have to rent a nissan/toyota etc.
Have fun!
FlashKiwi