Well, I own an R6 and I was a pilot for a while, flying 4-seaters.
Frankly, the environment within one of the cockpits and even hanging outside at 130mph should be no big deal for the Leica. I can't imagine that it would be a problem for the Contax, either. Unless the plane is outfitted for oxygen, he's not going to be at a high enough altitude for it to be really cold. So, I don't think the environment is an issue. My R6 is built like a tank and would certainly hold up. I've held an R4 a few times and it seems like it would handle it easily, too.
I'm not trying to convert anyone to Leicas (or Cessnas). I think either would do the job - so why not go with the less expensive one and spend the savings on extra air-time and barf-bags?
Once he trims the plane off, maybe he could shoot with both hands! Then he wouldn't need a winder.
Sounds fun. I recommend looking at the work of William Garnett.