Although the 757/767 series had a major FMS change with the advent of the Pegasus, the fundamental aspects are a design circa 1980.
Correct.
757 and 767 are the first of the "4th Generation" of jet transports, which the latest airbus and Boeing models all belong to as well.......but im sure you already know this fact.
Not even sure what you mean by that? So the A350/B787 are the same generation as the 757/767? Doubtful. What were the 3 earlier generations?