I have one datapoint, with a pair of SEKAI 4000 frames that are about one inch in difference and both are 1976-1978 frames, I believe. Unfortunately, I am missing the weight from one of them as the crankset is currently stuck in it. I will see if I can extract the crank and measure it.
http://www.ece.ubc.ca/
Another datapoint from that table is for a Raleigh Competition vs. International, 22.5 vs. 24.5, 1977 vs. 1971. The difference for 2 inches of size is 80 grams. Braze-ons and dropouts are comparable. The heavier frame has a stuck-on pump umbrella. One has chromed nervex lugs, the other has unchromed bocama competition lugs. Your mileage may vary, but I think 40 grams per inch might be a good ceiling for a 531 8/5/8 frameset in the larger sizes.
- Don (currently in Japan) Gillies
San Diego, CA, USA