Base camp is about 17,400 feet. At ISA the temp would be about -19, apparently it has been around 0-1 deg C lately. So lets say for argument ISA +20. Roughly 20,000'. QNH VNKT for a guess has been around 1009 so add another 120' or so. Could have been as much as 22,000' without difficulty, chuck in a liitle wind............
Serious stuff!