I'm either going to order a 3" cat back or order the parts to build a 4" setup myself. What do you guys think the pros/cons are to each?

NA for now, nitrous later... 1 7/8" lt's... all the normal stuff.

 

the 4" is loud...

I would probably go 3.5" if it were mine. Should be plenty of exhaust for a 5.3 even with nitrous. It will perform better when you arent spraying too.

 

Dual 3".....

 

Corsa 3.5" catback

 

I try to keep my exhaust the same size when running nitrous. The long tubes are a 3in. system- most cat backs are 3in. and the tips really don't matter.

My trans am full exhaust is a 3 in. system with an electric cutout for the track.

 

4" looks cool, it is loud, drone will hurt you with the wrong muffler, with either, but 4" is much louder. With a goal of n2o or FI down the road, and the cool factor, I went with 4".

 

This^^

Or single 4".