I know from experience when using Swiss powder that 3f has more velocity than 1 or 2f. But because I am using the same grain amount their is a little more recoil. Pressure for black powder isn't an issue as a 10 gauge is only in the 4500 to 5000 psi range. Goex and Elephant powder from my testing has the slowest velocity and also produces the most visible smoke. Old Eynsford and Swiss burn the cleanest and produce the most velocity if that is what you are after.

"As for me and my house we will shoot Damascus!"