Big Single exhaust?

Oval tubing. Run a single. Sounds smoother, more noise cancellation and possibly more torque or broader torque curve due to velocity.

My f150 had single with 3 cats and a muffler. 1 cat off each bank and one after the Y. I just took off the back cat and muffler and ran a straight 2.5 from the back of the Y to the rear bumper. Sounded smooth and mellow.

Ive been seriously debating it on my machine. HP max on single tube concerns me. The oval helps seriously on ground clearance and max tube size but you are going to run it under the rear end rather than over unless you have a master tube bender on hand.

Neat company with lots of exhaust goodies:

http://www.spintechmufflers.com/tubing-oval-round-transitions/oval-tubing/cat_41.html