I was aware of the Scharnhorst tests, but didn't realize they addressed the 12lber versus 6lber question. Really need to pick up Dawson, Dawson, and Summerfield and augment Hughes.
I've been trying to figure out why the Russian used so many 12lbers. I think I need to turn the question around. Perhaps the high proportion of 12lbers, half of which were the poor overbored 6lber "small sized 12lbers", explains why the Russian preponderance of artillery did not seem to be felt so much on the battlefield.