GMR has posted some great info here
I agree with Steve, it's all about the curves
OP, if you want some big muscle, install a Trask Turbo...
or if you want the bike more responsive everywhere, a Baker DD7 (if you're the type that just wants to putt around in 6th gear all day at 2k rpm and just roll on to pass, then a DD7 is a waste of money for you...)
Me; The curves of the stock 255s didn't suit my riding style (all left, no right) the 259s were much better for me ( less left, more right). I "backed into" a 117/DD7 (when a failed lifter grenaded the motor) and am not looking for any more for the way I use the '09 SERG - "Sport Touring".
The '09 is a very happy medium for me, does everything well...
When I want a bike to go sideways when shifting into 2nd or 3rd I hop on the '01 Switchblade...
Past a certain point (of power increases) the bike will become more "one dimensional"
Steve has the 113s dialed in, a great combination!
If any bottom end work is to be done on your existing motor, the S&S 124s are an extremely cost effective package...