Did your "friend" really sit in the back seat of an F3?
Certainly possible in theory, as F3's were zoom climbed to above FL700 I believe during initial trials,
However, these aircraft would have been very different to fleet aircraft, and I certainly have never been that high personally.
If he'd been chasing Mach 2.15, I wouldn't be surprised to hear a 'double hush' of the fuel starvation variety
