Im not sure on what would perform better:
Pacesetter LT's with cutouts on header into 2.5" Dual in / Dual out magnaflow with built in X pipe with either turndowns or out the side like it is now
Pacesetter LT's with ORY with one cutout into 3" single in / 3" dual out magnaflow with either turndowns or out the side
i dont know if it would be better with one cut out or two either. all the truck guys run duals and all the car guys run ORY

 

Ive always heard that a single 3" will flow more than dual 2 1/2's. But I like the look of dual comming out the rear.

 

It really depends on what you have done. I like the sound of true duals better, but for my supercharger I need all the flow I can get. Dual 2.5 will outflow single 3 inch but to see anything you really need some mods.

 

i took this from a thread written by literddevil......it is some good infor to help you out with singl 3" or dual 2 1/4".....i personally have a 3" in 3" out on my 02 5.3L......

2" is 3.14 square inches
2 1/4 is 3.98 " "
2 1/2 is 4.91 " "
3" is is 7.07 " "

You can see going from 2.5" to 3" increases the pipe size by over 40%.

 

The car guys have no choice but to run one pipe (ground clearance) Run duel 3"... flow like a mother F'er. Look at it this way. If you're doing cut outs, you want the flow. Right? To hell with 2.5" this aint the 90's anymore.