The old rule of thumb used to be 45 caliber and under they used 3f. 50 caliber and over they used 2f. I always considered the 50 caliber a middle of the road caliber. You can use either and get good results. I use Goex 3f in my 50 calibers for the most part. Especially the flintlock rifles. I also use 3f Goex in my inline rifles because I get better accuracy with some projectiles.

I even shoot 3f in some of the .54 caliber rifles. All you can do is try the two and see what gives you the best accuracy. I really would not worry about a little extra boost in pressures to the projectile. Also there is some concern that shooting the hotter 3f powder can ring the breech of the rifle because of the higher pressures. I have no evidence to back up whether that happens or not. The main thing is use the powder that gives you the best accuracy.