In my experience, 10 yards to 40 doesn't change much with moving to higher elevation, maybe a click or two, or if using holdover, not even enough to separate the effects as being from human error or the elevation. So the guns zero is typically fine too.
Where it does seem to matter are the 40 or even 45+ yard shots. At elevation, shoots a bit flatter so impact points are a bit higher than expected. Down in flatlander country, shots impact a little lower than expected.
For reference, I live just under 5700. The high elevation matches I typically attend are @ 8200 (Aspen MTN matches just south of Luna, NM with Southwest Airgunners), 7200 (Mormon lake matches just south of Flagstaff with Airgunners of AZ). The low country matches are at about 2000 (Phoenix airgun club @ Rio Salado), and then whatever Phoenix Rod and Gun club is over by South MTN, guessing between 1500-2000 also, and then I've shot @ Ben Avery which is around 1200 if memory serves.
Really, for a PCP, high elevation makes em shoot just a bit flatter, but it's not what I'd call drastic. And the effect doesnt even seem to be due to fps changes, more just the air density. Now, springer is whole different ballgame. I lose around 30fps shooting a springer @ 7200 from 5700. I've not even tried the springer fun @ 8200.
