Flying, for example, to Mexico City, the landing elevation will control the schedule and when established in the cruise, the cabin will be scheduled to destination elevation.
Only airport I have flown into where the air quality in the cabin at altitude was significantly better than on the ground (not the only just the worst), I started tearing up about 2000' agl.
Oh and R2112, I was going to leave that one alone but just about everyone I have spoken to that has not been there thinks that Lima is a high altitude airport. Used to love flying in and out of that layer of fog that persists for a good part of the year. Nothing like climbing out of that muck to see a full moon illuminate a sea of fog stretching into the Andes.
Another nice leg I used to do was Manaus - Lima. Over Lapaz, lake Titikaka and some very rugged terrain, great sight seeing.