There are actual studies on this stuff based on the changes in U.S. federal speed limit rules in the 70s and then again in the 90s. They are not conclusive but do suggest that higher speed limits lead to more fatalities: https://en.wikipedia.org/wiki/National_Maximum_Speed_Law#Saf...
More people died in Montana after they were forced to put real speed limits on the roads, with police enforcement: https://www.motorists.org/press/montana-no-speed-limit-safet...
The German autobahns are extremely safe compared to their other roads. The US interstate system can easily support "Reasonable speed limits" on most of their roads - its flat and straight.
These studies don't take into consideration what actually happens when some people decide to follow the law and some people decide to travel at the road's natural speed. That delta is the cause of so many accidents.