Drew H, thanks for taking the time to post this detailed info for me. Seeing it quantified helps:
On introduction in 1907 the 20g hangtags specified 2 1/4 Dr.Eq. with 7/8 oz. shot (1155 fps); later 7/8 oz. 2 1/2 Dr.Eq. (1210 fps).
Though pressure and recoil MAY be correlated, it is recoil that cracks stocks.