J-
I don't think hand flying a heavy jet at the top of the envelope is very useful. Its not like you can do any aggressive maneuvering. The whole objective would be to stay smooth and not induce any wing loads whatsoever. If you needed to turn, you'd do it as gently as possible.
My "heavy" experience is with the 767 series. 200,300, and 400s. Its a very forgiving airplane. Boeing gave it a robust wing. Having said that, you can still get that "balanced on the head of a pin" feeling when you are up high and you get some turbulence or mountain wave. Its not really something you "feel" through the yoke, though. Its more from watching the airspeed and power settings and kind of a "seat of the pants" thing.
The 767-400 avionics has very good high speed and low speed buffet limits displayed on the airspeed tape. When those "hooks" and "zippers" start to close in on you from above and below, it definitely makes you uncomfortable.
I've had a couple flights over the years where we told ATC "we need to descend. NOW!" because the mountain wave was pushing the envelope beyond my comfort limit. I don't know anybody who has actually had a loss of control. It has happened though. An American A-300 had one a couple years ago if I recall. Lost a lot of altitude and some empennage parts before they got it back.
Now the MD-88 -- that's another story. They are pigs at the top of the envelope. The wing on that airplane is designed for a DC-9 and its barely adequate at 3700 ft let alone 37,000. 
Boeing builds airplanes. McDonnell builds character.