Soon after the first Autobahn opened up back in 1933(!), the road was littered with cars whose engines had given up the gohst one way or another. This (of course) was not acceptable, and the auto making industry soon set out to correct this. As you stated they seem to drive very disciplined, and that is how they make their cars. No elongated holes to make up for poor manufacturing of sheetmetal for instance. Over here, the Highway act that started the whole Highway kitnkaboodle was enacted in 1955, some 22 years later giving the Germans a headstart to say the least, since they by then had quite a few years of experience under their belts; especially when it came to engine and suspension design for high speeds. The average speed on an autobahn, as far as I remember it was around 130kph (81mph), this speed was driven in the RIGHT lane, unless you were going to pass in which case you very carefully looked in your mirrors to make absolutely sure you didn't see anything coming your way in the left lane. One thing that the "high speed" drivers usually did ( for protection and courtesy) is if they were traveling well over 100mph they would leave on their left turnsignal, which could be easily spotted. Myself the fasted I drove in the left lane was just over 224 kph (139mph) for about 45 minutes...I was late getting to the airport This was done in an Opel Senator 3ltr. inline six and the petal to the metal.
Ford knows that you are not going to (most likely) go over 100mph, so they don't have to put anything fancy into the suspension. After all a Crown Vic. is driven mostly by the 50+ folks, who for the most part are not known to be speed demons.(Especially in Florida!!!) As far as driving your 420 over here, I would say it would depend mostly on the road, the traffic, and your tires.
Have fun!

------------------
03/83 300D
07/73 280