The old Lyman charts show that for a 43" .45 barrel [from memory] 60 gr ffg is just under and 70 gr fffg is just over 1900 fps. That is what I based my guess on that my 65 gr fffg load out of a 42" barrel is ~1900 fps. They used Goex of many years ago now. Barrel length has an effect, but not uniform or always predictable, on velocities all else equal. Very generally speaking the longer barrel gives better velocities all else equal. But such things as patch/lube/ball combos, type of powder, rifling, etc. also affect results, so it is hard to compare one guys to another's...If you plot increase in powder charge against velocity for any given ball size I think you will find that there is a point of diminishing returns, where it takes allot more powder to obtain a smaller increase in performance. I try to find an accurate, powerful enough load that is also an efficient load--and that for me is typically on the lighter side of some folks pet loads. Pet loads are just that and noone should criticise someone's pet...
P.S., I believe the old Lyman charts were done with percussion ignition...