I tried at first to use 2Fg as a main charge in my .50 and 4f for the pan. It was sooo tedious for me, I decided to keep it simple. I switched to 3Fg in the main charge and the pan. It did burn cleaner, and I got more consistent chronograph of the muzzle velocity as well. I don't use what I consider a "large" main charge. The state minimum load for deer is 60 grains of whatever granulation that you use, so I tried 70 grains. It worked quite well back then, and I was using a .50 at the time. When I switched to a .54 I simply used the same bag and powder-charger. Worked fine, and has killed a lot of deer.
I think the recoil increase would be nominal. While the manuals all differ for when they recommend one switch from 3F to 2F for the main charge, they agree that there is about a 10% increase in results with 3F over 2F, right? 10% higher velocity should mean only a 10% increase in recoil, maybe?
Now the perceived recoil is another matter. All of my rifles and muskets are very wide at the butt. So backwards impact is spread out over a wide area. IF I was using a rifle with a much thinner butt plate, especially if it was metal and very crescent shaped, I might feel the recoil more, due to more pounds per square inch on my shoulder due to the reduced surface area in contact with that shoulder.
LD