I use FFP mildot reticles and memorise their points of impact out to 5 mil's of drop, which vary from 750-900yds. However, whether I take a long shot depends mostly on the weather conditions, size of animal, nature of the game, type of vegetation and surrounding terrain. Whilst in some circumstances I'd be happy taking a 850yd shot, in another set of conditions I'd insist on being inside 400yds, and do by best to get closer than 300yds with the same rifle. It's a question where ethics are as important as science in finding a definitive answer.