From our Bimmerfest friends we got this map with Autobahn speed limit.
I was very excited to stumble upon this map showing the restricted and unrestricted stretches on the autobahn system. 70% (according to ADAC) is unrestricted.

Here's the map: http://www.autobahnatlas-online.de/Limitkarte.pdf
Here's the legend to the map:http://www.autobahnatlas-online.de/LegendeLimit_e.pdf