Mallafets I'm not aware of any studies that have been done into that particular area. I can say from experience that I doubt there have been changes in average size as there is still such a wide range of heights out there. Weight would be an interesting one, but I think it's a relatively modern phenomena to weigh horses as much as they do now.
Stick, this is what I've found for you, it's not much I'm afraid:
Lady Gloria (2004 Diktat/Tara Moon) Raced 20 times, won 6, including a brace of G3s, on ground ranging from good to very soft. Finished a creditable 5th in the Prix de l'Opera on her final start. She's by far the best progeny of her dam to date (dam unraced, produced 4 winners from 5 runners) and the further family includes Queen Mary winner NADWAH.
Progeny:
2011 - slipped foal by Dalakhani
2012 - slipped foal by Dalakhani
2013 - colt by Royal Applause (vendor buyback at 45,000gns as a foal & vendor buyback at 38,000gns as a yearling)
2014 - filly by Royal Applause
2015 - no recorded covering in 2014