only some spaces of the autobahn are unlimited but the fines for even small things are insane.
you get fined into higher multiples of hundreds if you
1 - have a flat
2 - break down
3 - run out of fuel
4 - cruise the left
5 - eat
6 - smoke.
and points on license too - a license there costs thousands of euros.
point is - speed limit is provided for a reason. Anyone breaking it at twice posted speed should be considered criminal at sight.