All I can say is that I have ridden on the Autobahn a few times and it’s hardly ever really safe to go much faster than 220 or maybe 240kph; too much traffic, cars, etc… around. Now, I don’t live in Germany and I certainly only drive there on vacation or whatever about once, maybe twice a year so I am not saying my experience is representative, but it is my experience over several years that I have been there. If there are absolutely no cars around and visibility is adequate (meaning daylight) you may be able to push the car to the very “delimited” limit of around 300kph. Not even then do I feel that its “safe” but at least you will only kill yourself if something goes wrong. So good luck and try to record your next run when the cost is clear.