I'm curious about your options. If you want to stay with a Diesel, a 98-99 E300 will mind the altitude less than a 2.5 turbo. In my corner of the country you can get a 94-95 E320 or E420 for what 2.5 turbos go for.

For perspective, I can feel my 87 300D working at altitude more through the temp gauge than though the seat of my pants. Heavy throttle application sends the gauge to 100*C in short order. Fortunately the cooling system sees that the engine gets no hotter. Since it has a #14 head, I'm very sensitive to such things, but no aluminum head Diesel likes to be overheated. charmalu would advise you to consider a 617 turbo for altitude.

Sixto
87 300D