I think the answer lies in experience and practice. When I first started shooting I based my longest distance for shooting game on the conditions to hit a 9" paper plate consistently. I'm not sure that 100% certainty on a long range shot can ever be achieved, but with enough trigger time and experience your instincts with each opportunity at a game animal seems to take over, and be the best guidance. The greatest advantage of the long range hunter is that the distance capability provides you with far more options to change the variables to your advantage. If in doubt, I try to get closer, wait, change position, or pass. IMO