This is probably what I'm going to end up doing but just wanted to get some opinions from others who may have shot 40 cals. Ken Campbell suggested shooting 5 shots at 100 yds. I can't find the target right now but I didn't throw it out and If I recall correctly, I shot 3 shot using 50 gr and 3 shots using 60 gr. Just as you might suspect, the 50 gr charge hit about 2 inches lower than the 60 gr charge.
Granted, Kentucky windage can be used at 25 and 50 yds after it's sighted in for 100 yds but. The rifle will be used exclusively at rendezvous by it's owner, my daughter-in-law. Shooters have plenty of time to observe their target and load accordingly. Granted, in the field, aiming high will suffice but at rendezvous, hit are points and points are score so varying the powder charge works quite well.
If and when I'm using one of my 54 calibers, if I'm hunting, their loaded with 90 gr of GOEX, a .530 round ball, and a 0.015" patch. If I'm at a shoot, then that load is reserved for 100 yd shooting and all closer targets get 50 gr of Powder instead. It works great by the way. Over the years, I've discovered my poor old bones don't like a 20 shot trail walk using that 90 gr charge. I stopped using 54's at rondy's and took up 45 flinters. I'm not half as worn out at the end of the trail as I was shooting the 10 pound 54's.