The 727 was designed to cruise at Mach .92, but then the 70s gas crunch hit and everybody throttled them back. Nobody throttled them back up after the crunch was over (Should have been a hint to Boeing regarding the Sonic Loser.......people do not want to pay more money to save a little time). I have flight test video of the 727 at mach .97. Somebody around here posted a pic of their 747 at mach .91 and it was shaking pretty badly.