interesting theme , i just looked at the FOM of our turbo-seneca, one ac type i ride in our company .
maximum range is reached due to the book at 45% power. this setting aims for roughly 125kt indicated airspeed ( TAS depends of course on altitude)
the best glide speed at this plane is just 90 kt IAS , so max range occours far above this speed.
when we come to ( especially turbocharged) pistons you have to consider one more thing that was not mentioned and is unique here.
at low power settinngs you can lean out the engine aggressively, at higher settings you have to enrich.
since at high settings you need exessive fuel to cool the cylinders and keep the EGT in a range what is healthy for the turbo SFC and fuel flow is not nearly linear vs power output-at a turbine this feature does not occour.
looking at the book you see it clearly: the range difference between 45 and 55% power is nearly nothing, at 65% percent noticable lower, at 75% significant lower and at 85% ( the highest recommended cruise at the continental TSIO-360) dramatically lower.
the reason is that at up to 55 percent you can lean hard, above this not anymore, and at any power setting above 75% continental calls for full rich setting. ( especially with the altitude corrected fuel injection system on this engines )
best regards!