I didn't even know Zeros could fly high enough to cross Mount Everest or K 2!
Looked up Zero's and they could reputedly get up to 33'k/10km...
"Hump" missions were lower... mostly flying
around or into mountains was the result...
The Sunderlands were operating at around 10'K/3km on those missions mentioned (13 successful, taking out 537 sick/wounded/injured) and up to 17'K/5km approx (above rated ceiling height) for one other specific mission I'm aware of...
"Hump" flights were around the upper range mentioned above, iirc
C47/C54 ceiling is around 23'K and the C46 up to 27'K; B25 to 24'K and B25 to 28'K