I have both the 1 in 48 twist and the 1 in 60 twist barrels and I shoot only the round ball. What I have seen from the bench is this; at half charges in the .54, both with 2F and 3F, they both shoot about equal. But when the charge is increased the accuracy of the 1in48 begins to fall off.
The point where I see it begin in mine is 85 grains of 2F. For every increase beyond that the accuracy gets worse. That said, 120 grains of 2F still gives me a load accurate enough for hunting.
In the 1in60 I shoot 40 grains of 3F for target and 80 grains for hunting. My targets show no loss of accuracy with this increase. Granted I haven't done the amount of testing with this barrel but I have done some with both 2F and 3F. 80 grains of 3F is a fairly hot, fast load and I am very happy with results, both on paper and game.
For heavier charges, if given the choice, I would go with the slower twist barrel. I think a better compromise is about a 1 in 56.