We're seeing a trend here lately for trying to maximize the performance of a round ball. While it is good and commendable to want to stop game as efficiently as possible, it is not something a round ball is designed to do. Like teaching a pig to sing: it just wastes your time and annoys the pig. Within the limitations imposed by open iron sights a roundball does very well. Through the life of round ball rifles it has always followed that if you want more energy, you shoot a bigger ball - not the smaller ball faster. With your .54 cal, adding 10 grains from 60 to 70 will give maybe 125 fps more, but going from 110 to 120 will only add 50 fps. It is a diminishing return. In addition, the ball is held in a cotton patch that can only take so much before it fails.
I used to shoot 120 gr. FFg in my .54 when I was young and eager. Now, I use 90 gr. FFg. With FFFg I would drop back to no more than 110 Gr as a flat-out max, and 85 for most situations.
It is a primative projectile. That's why states give it a special season. You have to be a hunter and not just a shooter to get into the round ball's effective range, not just keep adding powder.
To give a maximum safe load for a specific rifle is a spooky preposition. Has the rifle ever been "rung" (fired with the ball not fully set, causing a bulge in the barrel)? Has the breech-plug experienced any corrosion not visible to the naked eye? What lube is being used? Patch thickness? Accuracy of your powder measure ( I have one that throws 25% higher with FFFg than the calibration marks read!)
Dixie lists the 1887 proof load for a .54 as 164 grains. That means if the gun swallows this once and isn't damaged in the process, it was approved as safe to shoot. That doesn't mean it can live on that load, or even repeat the process five times. Just that once.
The Renegade, IMHO, is one of the strongest muzzleloaders ever produced in either .50 or .54 calibers. But why expose yourself to dangers if it is not necessary. I would recommend no more than 120 grains, and I would suggest much less. 100 grains and a well placed ball will kill anything in the lower 48 within 75 or 80 yards. If you're looking to stalk and kill a grizzly from 15 yards with a single shot, you might want to consider a larger ball, like a .75, and that insurance the duck sells.