Having personally built frames from Ishiwata, Columbus (SL, SP), Reynolds (501, 531, 753), and Tange (#1, #2, Prestige) as well as other tube types, I may have some direct experience you don't have. The most significant metallurgical advances since the 1980s come as a result of changed manufacturing methods. In the 80s, most frames were brazed. These days, most are welded. The new steels from e.g. Reynolds and Columbus are optimized for welded construction. The older steels, including heat-treated steels like Reynolds 753 (heat treated 531), Tange Prestige (heat treated Champion #1) and Columbus SL/SP lose a significant degree of strength when welded. Reynolds went so far as to refuse to sell 753 to builders who could not demonstrate (via a destructively tested sample) competence at low-temperature silver brazing. Ishiwata tubing was not heat treated; AFAIK, the major improvement Kaisei has made over the original Ishiwata tubing is heat treatment.