Again welcome to the family, the 929 is a great bike. I put on a D&D slipon, it sounds really good at higher RPMs, but it doesn't compare to my old F4 that was loud as he$$. My buddy has a Leo Vinci on his and the D&D is louder.
As for losing hps you have to do your homework. D&D told me that their slipon adds 6 hp, but I haven't dynoed yet. My buddy with the Leo dynoed at 127.8 hp, but didn't dyno without it. I can assure you that these slipons add hp.
00 CBR 929rr
95 Camaro Z28