Congratulations. You are going to be looking at bullet weight and the diameter anyways. That being said why not look at energy per grain or better yet... it’s impact velocity.
A specific Hornady SP of unknown diameter and weight has 423 ft lbs energy impacting a deer. Does it have enough energy per grain to expand? Would it help to know the velocity?
Not all 1200 ft/lbs projectiles reliably expand as soft points, it really depends on velocity. Many cup/core soft points expand reliably between 1800-2000 feet per sec at a low end, or if you wanted it converted in to ft/lbs per grain it would be 7.2 - 8.9 which is pretty silly when you can just use velocity as a guide. The total number of ft/lbs is pretty meaningless. The best is when people start talking about how many ft/lbs it takes to kill a deer or elk.
Comparing cartridges, not bullets, a chart with only velocity isn't helpful. And to the 500 yard distance, all compared have 1900+ fps. If you added the weight, I can see a 338 is "twice as powerful" since it pushes twice the weight to the same speed as a 243. But when the velocity is different suddenly it's a lot harder to visualize. There's no such thing as one "magic number" but kinetic energy is the best starting point. If people think it's supposed to be the "magic number", and complain when it turns out it isn't, that's on them, not physics.
