(edit: and It's not like everyone is cruising along at or above the limit. I pass a lot of cars in free flowing traffic when driving with cruise control on at 120)
The 80kph roads that are double track with grass down the center are a ... fixture of the Irish rural environment.
But most of the rural 80km/h road strands are too dangerous.
The only purpose is to be able to give tickets to take money from people.
Most traffic in Germany, even in the unlimited sections, tends to max out around 130. France tends to hit that 130 and not go above it.
I stand by 120 as a generally reasonable speed for a motorway with a speed limit.
Austria, Hungary, Romania, Croatia, Italy all have 130 km/h speed limit on highways.
Where I live the upper limit is 120. If you drive at 120 people won't stop overtaking you. It's done this way because they have those mobile car radars to give people tickets when they need money.
The limits were higher, then Carter made then 55, nationally. Montana used to have "Safe and Reasonable" as a daytime speed limit. During 55, it was forced to be that, but it was widely ignored and there was a $5 fine for "Excessively Utilizing Natural Resources". People would hold a $5 bill out the window when pulled over.
I don't even have a rebuttal for a statement so demonstrably untrue. Speed limits were in place for decades before the 70s gas shortages.
And the limit on backroads is reasonable considering that oncoming traffic is passing by you mere feet/meters away.
It seems entirely reasonable