I ended up going with the 4" Rineharts. I bought them from Jamie at FuelMoto. They sound a lot deeper than stock, and a little bit louder. Now I'm considering new head pipes, but I'm going to need a new air cleaner and programmer at the same time. Those stock head pipes with the cats, must be horribly restrictive.
Right now I'm considering either FuelMoto's 2-1-2 pipe, or the Vance and Hines Power Duals. I really like the idea of the cross over chamber, to help equalize the two pipes.