A few years back, I rode in an Alitalia 777 to and from Europe, we took the Polar route and were anywhere between 39 and 50 thousand for the most part.
The air quality was fine and the cabin temps were nice. Actually, my only complaint with the airline, was giving me only 9 minutes to get from one end of the airport (Rome) to the other during a transfer, on my trip home. Needless to say, I didn't make it (they had just closed the gate) so I ended up getting home a day late.
Now the air quality at the Rome airport was horrible...it was warm and brutally humid.