My two cents...

Flowmasters are really loud - you may be shocked at first. I certainly was when I put my Flowmaster 50 Delta in with 2.5" piping. It softened up as it filled with carbon, though, but it is still very loud from 1/3 throttle on up (I feel Joe's pain!). The idle burble is awesome-sounding, though!

I think Kenny is dead-on in his assessment - it gets loud in back. Some sound deadening in the back of the VX should go with an exhaust upgrade (one of my summer projects).

But if you upsize your piping and go with an "unpacked" muffler like the Flowmaster, you will notice a difference in power. It's not hp you're gaining (those come at higher rpm), it's lb-ft of torque off idle that you gain with the less-restrictive exhaust, and I noticed it immediately as I pulled out of the muffler shop when it was all done. I went from chirping the rears inside tire to chirping both the front and rear inside tires.

Good luck!