Exactly, and I dont think anyone knows the answer to this, whether they claim to or not. The reason arrow weight isnt proportional to speed loss, is because a heavier arrow will absorb slightly more energy from the bows potential energy, making the loss of speed not as great because it has a slight gain in initial energy over a lighter arrow. Extremes in either direction make using ONLY the momentum or ONLY KE to determine this pointless, like you said...its all about a balance between the two. Most hunting weights will fall into the acceptable range, if you arent getting pass thrus into the dirt, assuming this is better, then Id look to a smaller Diameter COC head than a 2" rage, if you are happy with having bigger gashes and the arrow remaining in deer, stay with the devastating rage. At over 70 ft/lbs KE, you are nearly double the required KE to deer hunt....I think ANY arrow weight would suffice.