NG wing is based on the 757 so can go a lot faster than .82.
I was told that the -NG's wing was actually a scaled down 777 wing when I did a conversion course in Seattle. The engineer went on to tell us that R&D funds were fairly tight as it wasn't envisaged that the -NG would be a big seller, but that in the engineer's opinion a bit more time and money spent on the -NG's wing would probably have yielded 777 speeds! I guess we may never know.
I also remember reading somewhere that the tailcone section is an area of high drag on the original 737, hence the proposed re-design on the 737 MAX.
I recall flying with a Capt. years ago who would fly at the max CI (200?) on the classics on the last flight to get home. You could certainly feel a "rumble" from the wings, was that Mcrit over the wing being reached? I don't know!