I do not think my M7 will ever see the top of the Mt. Everest
But indeed there is a lot of difference with camera's under difficult circumstances.
In the past my EOS gave up at -22 degrees C. and my M645 Pro did it till the beginning of the night at -27 degrees C. I was already afraid that the film emulsion would tear off or so and further it was already impossible to use it afterwards, because my hands were too cold already to operate with the two camera's.
Leica M serie's are nice camera's and I do not think you will find something better in RF 35 mm. But best quality has it's price. Unfortunately this is quite high for this nice piece of German craftmanship.