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The idea is that the turbos allow maintenance of sea-level MAP up to the critical altitude. I don't remember off the top what that is, but the POH says full 32" MAP can be maintained by the turbos well above 20K' - you have to manually pull it back an inch for each 1,000' over 20,000 feet becuse of operating limiitations (the 30,000' chart shows maximum 22" MAP). The single engine service ceiling under worst conditions (rear engine off and feathered, 4300 max. gross) and at 20 degrees C is 17,000 feet. Few other light twins can match that, even turbo models.
Ignoring density altitude and per your theoretical situation: at 5,000 you might not have more power and thus staying at 5,000' would seem similar if it's not summer or otherwise hot - the big factors are that you can go higher to clear something even with an engine out - not being limited by the normally-aspirated lower single-engine ceiling, and if you were higher in the first place, you won't drift down to the vastly lower single-engine ceiling of a normally-aspirated model.
Being in the western U.S. definitely means that a turbo is an advantage. But if you live
elsewhere and simply wanting to fly around some mountains like the Appalachians or go west or whatever, what then?
An additional big factor is that you can take off in the heat of the day at just about any airport around. I've calculated density altitude at 6,000+ feet airports and always had plenty of capability and room for takeoff in the peak of summer heat with 4 adults and full fuel.
Claims of higher maintenance from turbos are greatly exaggerated IMO. Both of my engines went past TBO with no turbo problems (I had to once overhaul a turbo controller for $800 but don't consider that very significant and that's a normal maintenance item on a long-term basis). Nor have I experienced any exacerbated maintenance due to turbos. I treat the engines well, cool carefully upon approach and landing, and always run them at low speeds after landing to cool oil in the turbos. I've never had a problem.
I take off at 4450' and climb at 28" MAP / 2600 RPM / 14.5 GPH up to 8,000' or more practically every time I go anywhere, so it would be "28" if I were to quote anything at 5,000 feet.
I realize that normally-aspirated Skymasters work for many, and they are great planes. But beyond just the terrain of where I live and fly, I want to go when and where I want to go. I wouldn't even consider owning a normally-aspirate aircraft except for some specialty like aerobatics, etc. For the same reasons I own a Skymaster with deicing, oxygen, a nice package of IFR/GPS avionics, and have kept myself IFR current for years.
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