Am I correct that you want to identify at what yardage, with your trad bow-arrow, you will obtain equivalent penetration that you get with your compound bow-arrow at 40 yards with comparable arrows? If YES, . . . is it possible to create one or more types of penetration test targets?
Then shoot your compound at 40 yards. However much the arrow penetrates, that is your standard. You've told us that.
Using your trad bow-arrow on the same test targets, shoot for penetration. Move the target farther from you in increments until your arrow achieves identical, or nearly identical penetration. That's your trad bow maximum.
Since it's unlikely your test target will be a side of beef, hide on, you may want to consider "hard" and "soft" target tests. The main idea, though, is to identify "acceptable penetration" before you test the trad bow. And acceptable is whatever you say it is.
Just a thought.