In a prius yes. In a BMW with a 3L inline six, not completly. Those cars were purposedly built to cruise at 160 on the Autobahn. When you drive faster, you sacrifice a bit of fuel efficiency for some minutes gained on your final destination and a bit of thrill.
To be fuel efficient, drive a Diesel Passat at 120kmh. Nothing wrong against that. I guess you weren't advocating slow efficient cars driving slow anyway, I see your point.