I think that's a very generous assumption. Typical small engine light aircraft cruise at 70-120 knots (80-140 mph). Wikipedia[1] suggests 211 mph as the current electric speed record (made in 2017). I doubt typical aircraft will be as optimised for speed as the one that holds the record. Increased speed causes exponentially increased aerodynamic drag, so if you want to increase range, slower speed [than your maximum speed] is the way to do it, not faster.

[1] https://en.wikipedia.org/wiki/Extra_EA-300#Variants