I write from my experience, many years ago, when I was flying a Brazilian built "Bandariante" which for all intents was an unpressurized King Air. It used PT-6 engines. When they were first produced they produced a little over 500 hp and over the years have evolved to produce about twice that. Unlike most turbine engines the PT-6 is not a fixed shaft engine. The "hot section" is not directly connected to the geared propeller section. Incidentally, the engine takes in its air from the back and exhausts it from the front, hence the big exhaust pipe right behind the propeller.
Now to confuse things further.
Some Pratt turbo prop engines have "prop brakes" so that you can run the engine with all its accessories (air conditioners, electric generators, etc) with out having the prop spin. That way people can work outside the plane safely, like loading cargo, with out being turned into ground meat.
Some King Airs were produced with Garret engines which are somewhat more fuel efficient. But most used the PT-6 which doesn't get quite as good mileage but in my opinion tolerates much more abuse. The PT-6 will run on virtually any flammable liquid as long as you can force it thru the fuel filter. That was a big plus, when the engine first came out, because one could easily wind up at some outlying airport needing to refuel and not have any idea what kind or quality of fuel you were likely to find.
I think this is as far as I'm going to drift off of this thread.
