You should pick up 100 to 150 fps. with the extra 2" barrel length, but the longer you make the barrel usually the less gain you get per inch if that makes sense to you. also, with the longer barrel, you may want to try some of the other slow powders out there. I don't personally have any experience with this round, but I have had good luck with retumbo. You want the slower powders with the longer barrels and heavy bullets so that the powder is still exerting force on the bullet when it leaves the barrel. Of course, not to slow that it's still burning when the bullet is long gone! Hope this helps.
you cant dump'em if you don't pull the trigger!