At Gwelo we were at approx 4,500' ASL - the day/night temp difference could be as much as 30 deg...which is great for cloudbase,I certainly know of definite 12,000' base in zim...although never quite got there myself
I think he flew out of Windhoek (sp?). Off to Oz in five weeks; haven't flown there but apparently the cloudbase is off the beserk scale, oxygen required, that sort of thing.