VMO / MMO on the 727 was adjustable, depending on zero fuel weight.
A switch labelled A / B mode changed this limit.
In A mode VMO, was 380 knots MMO .92
In B mode VMO was 350 / .85.
the Trident was certainly a fast ship and it sounds like you regularly flew them at the limit, in the 727 we rarely did as the fuel flow above .86 was horrendous.