Muleskinner, I think the approach you outlined (center hold for near range, adjusting hold for 100 yds) is a pretty reasonable one. For target shooting, your other option is a 'six oclock hold.' If you were only shooting bullseye targets, there might be some advantage when your targets got scored, but if you're going to be shooting paper squirrels, crows, nightmares, running foxes, standing and running chucks, etc, or if you shoot woodswalks with different size targets, being sighted in for a 6 oclock hold is a bit of a pain and a disadvantage.
The ballistics tables and programs I can find say that if you're sighted in for a center hold at 50 yds, you're going to hit 3 to 6 inches low at 100 yds, or you may find yourself holding high on the black. For paper targets, a lot of folks use a heavier charge for 100 yds to get more muzzle velocity and hence less drop out at 100 yds. Again, the printed data I've seen says bumping the powder charge up may raise the point of impact by an inch or two. (And, there are other variables, such as stock drop and how your eyeballs are calibrated that make printed tables just approximations of what's going to happen for real.) If your style of rifle and the shoot rules permit, you might look at a buckhorn or semi buckhorn sight and experiment with different sight pictures and amount of blade showing for 100 yds. And, find a load that gives as tight a group as possible before playing with the sights too much. SCL