[BFeller]

Autobahn speed limits and higher speeds in general are not possible with the current structure of the US. My basis for that statement is from my five years experience driving the autobahn in the late 80's to my current experiences on the Interstate system.
Drivers in the US Can get an oral test if they can't read. At that time in Germany - the student paid for his own drivers ed training. Cars in Germany were better maintained. An autobahn breakdown could result in a ticket. Here a car gets a 15 or 21 point safety inspection - they have a much stricter inspection. I saw a few art cars in Germany - not stuff held together with bailing wire. Drive right, pass left was more than just phrase on the Autobahn. Here, it's "I paid for the road, I darn well will drive in whatever lane I want."
As for graduated speed limits based on ability - any trooper ought to be able to tell you the dangers of speed differential in traffic situations. Traffic going 55 does not mix well with traffic going 90. See the drive right pass left statement and think about it. You go from cruising the left lane to having cars treated like moving autocross cones as they are dodged.