I've done kinda the same thing on earlier model touring bikes, but I did it in the primary with the S/E race package they use to sell. I don't know if there would be a real big advantage to lowering the gearing on a softail being a lighter bike unless you want it for trailer pulling maybe. Harley changed the primary gearing in 07 when they went with the 6 speeds, the engineers tried to set up the gearing so the average rider would be shifting in all the sweet spots on the rpm range in normal driving. If you do it let us know how it works out, you would also have to recalibrate your speedo if you do it.