I have a 2bros slip on for my 929. Its not insanely loud but it does have a nice basey type of growl. That was want I wanted versus the really loud kind. I'd recommend it. If you want really loud, I heard my friend's Ducati 998 with Vance and Hines exhaust. It was really loud. Not sure if that was because it was a v-twin or what.
Like they said if you want growl go for the 2 bros.. you want bark get a Jardine... if you REALLY WANT !LOUD! get a D&D. I have a D&D slip on for my F2 and its louder then any bike ive heard. As the rider you never really hear your bike compared to others and you may think they have a louder or just as loud pipe but believe me.. NOBODY at the recent dyno session was louder then my bike. I thought one guy on a 750 or 1k who stripped the packing from his pipe had me but come my turn half the people were backing away from the shop and the others were curious what the hell was on the dyno. Sounds awesome too.. Not the most solid sound but definately distinguishable between the rest. I love the way it sounds... its too bad i cant hear that when im riding it.
I have a T.B. on my F4 and it is very deep. I ride with an R1 with a D&D, a 900RR with a D&D, a ZX9R with a muzzy, and a TL1000R with twin Yoshis, and mine is the second loudest and deepest behind the T.L. I love the tone of my T.B. It sounds like you mean business. It's not hi pitched and whiney like the others I ride with. I'd go with the T.B.