Not sure how it would sound on the V10, but I had a Magnaflow 18" with duals on my old 360. Sounded good and didn't have the annoying cackle of Flowmasters. You can go with a 14" if you want it even louder.
I'd get on youtube and look up V10 exhaust clips to get an idea.
2001 2500 QCLB Cummins NV5600 4x4 - Fass Titanium 150 - 4" Turbo back w/ 4" downpipe - front and rear replacements - American Racing 16x10 - 33" BFG A/T