I have one Champion 2500 dual fuel generator and I live at 5000 ft in Colorado. I'm only running it on propane to date, and you don't need to re-jet with propane as fuel. It works fine for basic 110v maintenance needs at the storage yard, but it will not run the a/c. After watching my power management amp readings on the last camping trip, I'm not sure two 2500's would either, at least at 5000'. Do your homework carefully.
I've found my 2500 is very difficult to start on propane (I've never run it on gasoline, so I can't comment on that fuel). The support from Champion has been good, and they are sending me a new carb and stepper motor. In retrospect, I should have returned or exchanged my generator at Home Depot before the 30 day period for generators (I spent that time trying to solve my issue with support at Champion). There is a nice video on Champion web site on removing the carb, so we'll see how it goes.
After it starts, the generator runs smooth and pretty quiet.
I would prefer two smaller units over one big generator for my needs. I could not load / unload a 100+ lb generator into my RAM. I think the manufacturers reduction in capacity from altitude is pretty accurate.
My experience. Others may have more to add regarding theirs.
2016 Bullet 272 BHS
2014 RAM 2500 5.7 Hemi 4X4