That is interesting that he gained 300 fps with 9.5" less barrel. I think there was something else going on there besides just the choke. He might have lost the same amount even if the choke was improved cylinder instead of full. As you said, the true test would be to chronograph with the same length barrel and different choke constrictions. When you change 2 variables (barrel length and choke constriction in this case) it's hard to determine which variable had the most impact or if it was a combination of the two. With one variable, the impact of that variable is more easily determined.