For best range, you should fly at or just above minimum drag speed, which is substantially less than a typical light twin's normal cruising speed.
If you fly at
high power at
low altitude, your IAS will be aerodynamically inefficient, so range will be reduced. If on the other hand you fly at
low power at
low altitude, your engine will operate inefficiently. How much is gained by flying at
high altitude depends on the type of engine, whether it is turbocharged, and fuel burned inefficiently in the climb. It seems the Baron gains very little range by climbing to 14000'. Above that altitude I would guess the normally aspirated engine produces so little power that it's impossible to reach the most efficient cruise speed.
This graph seems to illustrate that best range is obtained at low power at low altitude (aerodynamics are more significant than throttle setting) and low rpm (reduced engine friction). Flying high will of course give higher TAS and perhaps less travel time, as you suggested.
actual horsepower delivered INCREASES if you hold the same MP/RPM with ascent, along with increasing fuel flow and increasing TAS
Yes, I think so. Since best range would be obtained at a lower power (for aerodynamic reasons), increasing power as you climb is reducing range. Once full throttle altitude is reached, power drops off rapidly with further climb and range increases rapidly.
Everyone learns in flying school that increased altitude results in increased range. The graph illustrates that real-world complications of aerodynamic versus engine efficiency complicate that to the extent that, for a normally aspirated light aircraft, altitude has little effect on range. It's a good question for a flight instructor initial issue test, to test ability to interpret a real world flight manual against a theoretical textbook.
Hope that helps.