From what Ive read,
323/328 is twin 2.25 inch pipes til 1st resonator, then single 2.5 inch pipe the rest of the way
325/330/ZHP is twin 1.5 inch pipes from cats all the way back. Everything I've read says this is soo much better than single 2.5 inch pipe, and is a much better design
You are right that Im not going to be getting amazing gains or a huge change in tone/ volume, but I just want a little bit (can't be too loud b/c of where I live). I am also looking for a cost-effective solution, and don't want to spend much over $300 for parts AND labor.
Ideas or thoughts? Thanks