Looks as if #5 is likely seamless CrMo that is strait gauge (unbutted) 0.9mm tubing. Is it a 26.6mm seatpost? If it is not Hi-tensile, it might actualy be a decent quality (but heavy) frame.The thick tubing might have been a "feature" intended for adding stiffness to a loaded touring bike. If you are hauling 40lbs of gear in panneers, the extra weight of the frame would be inconsequential but the extra stiffness would be much appreciated. I did a loaded tour on butted 531 frame years ago, I could easily shake the bike and make make the frame wiggle like a limp noodle when it was loaded, rather unnerving.