Not sure what you are asking. Better how? You might get some better responses on a GSXR forum.
I assume you have the S.E.T valve still intact. This would be a good thing if you just plan on adding a slip-on with out any after market fuel management. The S.E.T. will regulate back pressure for you in the low and mids. So any slip on you choose will only give you a minimal boost in power and probably won't be noticeable.
If it is loud you are going for D&D is in a league of its own. They have the capability to irritate a nun half way around the world.
As said earlier yoshimura has a nice sound to it. I have an aluminum RS-3 and it is a bit on the quiet side. Which is a nice thing. I originally bought it to cut down but grew to love the sound of it. Down low and in the mids it is nice and quiet but yet just loud enough to hear the engine at highway speeds. But when you downshift and get down to business it has a nice aluminum zap to it that is defiantly louder than stock.
Are you going with aluminum or carbon? This is a huge difference in sound. Aluminum has a tin ring to it that sounds like a F1 car, while carbon has a deep growl to it and roars like a drag car when opened up. I also have a carbon Jardine RT-5 that is nice and loud. But not ear piercing loud more of the hit you in the chest loud.
Also if you don't like what you get you can always pop the end off and either adjust the packing or cut it down and rivet the end back on.
I did a little reading on the Two Brothers V.A.L.E system and it seems the end easily comes off and you can alter it to what ever level you want with out any cutting. I have never tried one but it looks appealing.