In my Lyman BP Handbook for 12ga, fiber wads, 2F powder:
3.75 Drams, 1oz/shot- 1422fps
same but 1 1/8oz - 1355fps
same but 1 1/4oz - 1250
same but 1 1/2oz - 1100
Strangely enough if plastic wads were used velocities fell. Go figure that if plastic wads seal better there should be higher velocities - at least I think. Better stop doing that.