No matter how romantic it sounds to drive a powerful car on the Autobahn at high speed, my advise is to avoid the Autobahn as much as you can and opt for the French Autoroutes instead as long as you can! The Germans have dug up half of Germany's Autobahns and there are 'Baustellen' (Roadworks) everywhere, causing a lot of traffic jams. Belgian's motorways from West to East are not really much better than the German's. Added to that: Belgian motorways lack service stations. The few that are around, have ridiculous fuel prices.
Having driven 30K kms on Dutch, German, Belgian, British and French motorways during the last 10 months, I can safely say that the French are far ahead of the rest of Europe at the moment.
M.