Having had a very few 'discussions' with JL before, his points of view nearly always were at odds with others...although he most certainly did not want to discuss with yours truly the technicalities of the Lockheed L1011 (and especially the FMS installed therein) as clearly he was at a severe disadvantage, figuring that perhaps I had forgotten more that he would ever know about the subject...which I suspect was a true conclusion.
I cannot address the merits of the B757/767 as I have not flown these, however the L1011 was flown well in excess of Vmo during flight test, and indeed, considering Mmo, which for the TriStar is M.90, flight test was performed, according to Lockheed test pilots that I know...at M.98.
So, excess speed certainly is possible, but only a fool would go there....unless you were a properly trained test pilot.
Of course, exceeding Vmo/Mmo will sound the overspeed clacker, but simply tripping the appropriate circuit breaker would 'fix' this inconvenience.