My 'Personal Best" is 660 Kt in a B727 against a TAS of 480 Kt, a wind component of +180 Kt. Figured that it was the equivalent of M 1.1 in still air, and always pondered whether people on the ground could hear us coming or not.
My 'Personal Worst" is 320 Kt in a B777 against a TAS of 500 Kt, a wind component of -180 Kt. Over Japan of course, where else?