I got a Hunter FGA 9 up to an indicated 56,000 feet over Malaya once on a GH sortie. Only one to trail that day.
Tengah ATC wasn't too amused by 20 beeps in response to their request for one beep per 1,000 feet above 30k during the subsequent practice speechless flameout. But I did get in OK even though it took a long time.