O.K. Since you Guys have coerced me into this ....
As Barbagris has said you won't get over 150 RWHP whilst retaining the Stock header, but as you know, there's heaps there anyway, a slip on muffler, or two .... will enhance what you already have and run real well.
The first thing that I did when I first got my 06 Rocket was drop the CAT and three mufflers off and built a twin muffler system to slide onto the stock header.
This sounded real nice, and ran strong.
I now build this system with different mufflers. This will fit all model Rockets, I also have a version to suit the Touring.
I also build a Single slip muffler, as with the above twin muffler system, it is supplied with clamps, heat shield/covers and mounting brackets, all that is required to ....slip it on.