I have seen flight test video of a 727 flying around somewhere just above the cascades here in Washington during flight test that was running Mach .97. She couldn't have been more than 18,000 - 20,000 ft. Although it was not cockpit instruments I was looking at on the screen. This was a documentary flight test video and the commentator said "Here we have the 727.......Mach .97 yada yada yada".
The jist is that the 727 was flight tested to that speed. I am pretty sure that in recent times the 727 and the 747 have gone Super Sonic more than any other commercial aircraft.
Who needs the Sonic Loser when you could just make a derivitave of the 727 with nice quiet efficient engines?
Wasn't the first plane into the twin towers doing like 350 kts?
