From my understanding, the Cat/muffler box on this bike is what quiets the bike. When you change the header you also take away 90% of the sound reduction because you are removing the muffler box. In other words, it does not matter a whole lot which muffler (end can, silencer, slip on, etc.) you choose. The bike will be loud. Now that does not mean every slip on will be as loud or as quiet as the next. My personal opinion on this subject is the larger the slip on, the more noise reduction it should provide. But that is just a guess.
The Dude Abides and Rides:
2017 Suzuki GSX-R 1000-Blue