The suggested speed on the Autobahn is still 130 km/h. If you're going significantly faster and cause an accident, your insurance will probably consider you at fault and only cover what they're (edit: legally) obligated to.

Much of the Autobahn does have limits though :)

I drive in Germany sometimes and the roads are too busy to be going very fast, my average never got much higher than 150 km/h even if you only count the fastest portions. To be fair I haven't tried crossing the country starting on a Sunday at 3 AM, you can probably go as fast as is efficient to not waste time on extra refuelling because of the car's drag.