I am puzzled as to why you chose miles per hour as a unit of measurement when discussing speeds a turboprop aircraft can achieve. Isn’t the driving issue the speed of sound at the propeller tips? Doesn’t the speed of sound change as the density of air changes? (answer: yes to both)
So why state these speeds in terms of MPH? Why not Mach numbers? Don’t worry most people know how to convert…
Also, while discussing turboprops, please mention the fact that a turbocharged piston engine can actually perform even MORE efficiently. To prove my point: there are people who have re-engined Cessna P-210 aircraft with PT6 turboprops and discovered that while their speed and load carrying capacity went up slightly, their range went DOWN.
All that said, there is an advantage with Turboprop engines: You can burn the same fuel as the jet aircraft. No need for separate tanks of fuel.