bonanza- 10" at what range? 50yards? That's a lot and will take considerable sight alteration.
I would change both sights as recommented, thus halfing the difference on each sight. This will maintain fit of the gun better than making a big change to one sight.

I like Kuduae's recommendation.

Gatsby - would heavier load, ie: higher velocity bring the zero down, or raise it? Can the way the rifle is held, perhaps too lightly, account for the higher impact? In my .58 RB double, I noticed better regulation and elevation between the barrels stopped, when holding the gun quite tightly. Probably not at all the same with a ctg. gun of some value (compared to the poorly made Eyetie muzzleloader).