No not at all. The reality is the speed limit isn’t designed for fuel efficiency at all. At it’s best (ie when the transportation department is really thinking things through, this is usually in city driving) it’s designed for safety, at it’s worst (generally the freeways) it’s designed for revenue. Only during the 70s was anybody in charge actually willing to pretend fuel efficiency had anything to do with the speed limits, and of course according to the government organizations that pay attention to this stuff on the broad scope it really was all make believe, then they switched over to the whole “safety” thing but that turned out to be BS too (between the illusion of safety and increased road fatigue slower isn’t actually generically safer).
Lets not forget this, about the unlimited-speed (in most parts) Autobahn in Germany:
“The overall safety record of autobahns is comparable to other European motorways, and motorways are safer than other road types. A 2005 study by the Federal Minister of the Interior indicated that there were an equal number of accidents per kilometer on the autobahn in sections without any speed limits.”
Increased speed does not mean increased fatalities.