As for power I really didn't notice much, I'm barely at 600 miles on my bike so I have not really pushed her. The exhaust is probale the loudest on the market for the monster, I'm talking Harley Loud. I paid about $1100 with the ceramic coat.
I installed a small 2-3" baffle in mine... Helped a lot with smoothing everything out and making the noise bearable.. Not sure if the baffle increased power or not, but it made the bike feel better...
Also, a powercommander and tune help a lot since this is such an open exhaust and the bike runs least as it is