I think the record for breaking the sound barrier is still up for grabs and there was a very recent attempt at going for that record but it ran into troubles getting the required permits for the balloon ascent.
Kipplinger in project Excelsior got very close....but according to his own notes did not actually exceed Mach 1.
An hour and thirty-one minutes after launch, my pressure altimeter halts at 103,300 feet. At ground control the radar altimeters also have stopped-on readings of 102,800 feet, the figure that we later agree upon as the more reliable. It is 7 o'clock in the morning, and I have reached float altitude*... Though my stabilization chute opens at 96,000 feet, I accelerate for 6,000 feet more before hitting a peak of 614 miles an hour, nine-tenths the speed of sound at my altitude.[4]
I got thrown out of a Luftwaffe Transall once...so I can't even clim one jump but I know for a fact there is no way I would have signed up for the jumps Kipplinger made.
This man truly had the right stuff.
Cheers
Stefan