No not really, unless the older gun was in danger of exploding from the day it was made, or it has been damaged, assuming it was a properly made BP barrel. An antique barrel is something else, and a primitive barrel (hand cut threads on the breech plug) shouldn't be shot (imho).
Black powder hasn't really changed all that much in the past 150 years. The only real improvement was "glazing" with graphite. You shouldn't be pushing an antique barrel, or a barrel from an unknown maker, to max loads. Most of the factory made adjustable measures go to 120 grains (iirc).
So as you near max loads, 15% becomes significant, but for usual loadings the difference is not that great. So a 100 grain load in 2Fg would be similar to a 115 grain load in 3Fg, but an 80 grain 2Fg load is only 92 grains of 3Fg.
I use 70 grains of 3Fg in my .54, which would be only 60 grains if I switched to to 2Fg and used the same measure. I prefer using 3Fg as it works better for consistant velocities, leaves less soot, and works well as a priming powder.
I think the problem is that 4Fg is really not good for a main charge in a rifle, and when muzzleloading resurged in the 1960's, a lot of unchecked, antique guns were tried out, and several accidents occurred using large loads of 4Fg..., and folks today assume that if 4Fg is bad when you should use 3Fg, then 3Fg might be bad when folks should be using 2Fg..., and so on...
Basically, there is rarely a reason to max out a load in a BP gun.
LD