Cessna 207. If you were serious, you could make that work well, but what it really comes down to is good maintenance and care. I'm half-kidding about the 207, but piston engines are amazingly good if you take good care of them, like warming up/pre-heating, proper power and mixture management in the air and the ground, changing oil, inspecting fittings and replacing stuff, etc. I'm not adverse to piston engines, even just one, but I have a lot of experience flying them, singles and twins. Some twin-jet drivers may not be able to comprehend something that can't maintain 20,000 on one engine, much less something with only one engine. But as an Inspector, I've seen both sides of the coin as far as piston engines. Those people and airlines that take care of them have nearly bombproof service, while those that let things slide more and pinch the pennies sometimes walk the line of relying on basic certification and FAR rules to save them from themselves, which doesn't always happen. So if you are going to invest in an aircraft and do it right, I'd much rather invest in something with one Lycoming 540 or similar engine and put money into doing everything right with it and taking care of it, rather than being possibly spread thin with a twin with two engines and propellers and retractable gear. Unfortunately there aren't a lot of non-draggy piston singles that can carry that much except the Piper Malibu/Matrix or an old P210, but the Cessna 206 has a great reputation for being work-horse airplane and solid. Flying in the mountainous west, you simply need to plan your flights properly and not take ridiculous chances, which means you might get delayed every once and a while. Turbo is not necessary IME, but you need good experience with density altitude. Can be done safely no problem. Turbo brings a bunch of considerations and operating practices you need to do smartly and safely, from engine management to using oxygen, which can be more complication than practical. Most mountain, high DA and low-performance twin flying is all about ADM and planning, usually no stranger to most 121 pilots, except having to do it yourself, but usually quite different than many yahoos that figure their airplane will work for them at any time under any circumstance. A wise man said these situations are as safe as you make them, from the maintenance performed to your turn out direction. If the risk is too great, you just don't fly that day, rather than push equipment that is marginal for the conditions.