Depends on the prop and the plane..Our GT80 stock engines unload from 7500 on the ground to 9000 in the air..The race versions on methanol unload from about 9000 on the ground to almost 12,000 in the air...
Our 289 racing twin unloads from 7200 on the ground to over 9000 in the air..
We use data loggers and telemetry so these numbers are valid...