If you do choose to take the A5, make sure you take it southbound towards Frankfurt. The last section is a good couple of miles of straight 3 lane unrestricted where I have always managed to hit the limiter at 250kph!
Also the 32km between Frankfurt and Darmstadt are unrestricted and are know as the local "racetrack". Sunday mornings in good weather can mean a lot of the big boys out stretching their legs....fun if your are into spotting exotics


have fun and remember to slow down in construction sites, as the chance of your photo being taken are reasonably high!