I see some good responses already. So I will add my two cents. If you are not willing to practice out to the further distances you expect to encounter, then limit your shots to the distance you have practiced. There are people that are shooting out past 200 yards. While the modern rifles have that ability, many people do not. So the range of the modern day muzzleloader would depend on if you want to put a fatal wound on an animal or punch a hole in it some place.

As a side note, during the Civil War, there were sharpshooters with traditional rifles taking out people at 800 yards. Of course their objective was to only put a fatal wound in the target if possible. Still, there are reports of officers on both sides being grazed by sniper fire at distances out to 1000 yards.