I have read and subscribe to the " theory" as follows: Deer (North American) impact energy should be around 1,000 ftlbs. I have no experiance on elk but I would be humble to start at 1,500 for smaller bulls and cows and go up from there for trophy bulls. Since we are talking about impact energy might as well talk about caliber. Deer (North American) minimum of a .243 caliber 100 grain. Boar .264 caliber 140 gr. Elk (no experiance again) but I would start at 7mm 160-175 grain. Cartridge start at 7x57 and up through the magnums. I would not argue with others who would want more gun on larger " Northern" deer. More important is that the bullet design is picked for the right game, shot placement, bullet weight for game, and distance.