Lockheed has always built stiff winged airplanes. Witness the failures on C-130s and C-5s. The stiff wing is more efficient, but has to be far more rugged, and gives you a rougher ride. Douglas built a moderately stiff wing, and when you watch the swinging outboard engines on a 747, you wonder how they ever calculated angle of attack.
Nobody has mentioned Active Controls, computers that allowed the -500 to add more span without beefing up the wing.
As I mentioned early on in this thread, the DC-10 and 747 had sheet lead blankets to deaden the buzz saw sound on takeoff. I was told the 727 also had sheet lead in the sidewalls, until the fuel crisis of 1973. There is no better sound deadener.
GB