Well, to me, for my usues, it largely depends on what I am are shooting at, how far away it is, and why.
If this is a hunting load you are developing, I would be interested in seeing where it landed at 100 yards, what kind of game you are after and what you felt were the ranges you would be afforded shots, and were willing/able to take them.
Given the 85 yard figures you give in relation to the 50 yard ones, it is apparent the ball is past its peak trajectory and as round balls fired from a muzzleloader lose their energy rather quickly, I am going to guess that you are going to be pretty close to dead on at 100, and if your objective is to hunt and your game is something like a deer, then you are pretty close to maximum point blank range(MPBR), or the greatest distance which you can hold "dead on" and still connect with the vital zone.
MPBR helps while hunting when ranging may not be absolutely accurate as it gives you a good chance of connecting for the longest distance.. Your MPBR may even be good out to a little past 100 yds. depending where you print at 100. I don;t know about you, but the older I get the more difficult it is for my eyes to tell the difference between 85 yards and 105 yards.
Now if you are shooting paper targets at known ranges of 50 yards, 85 yards, etc. then I would consider replacing the front sight with an appropriately taller one, or even having a set of them for varying ranges.