Any opinions on this exhaust system?
I've read a lot about the 2.5 inch pipes people tend to go to vs 2.25
I'm looking for a little deeper sound and any possible other benefits from a newer exhaust. I do understand without headers the newer exhaust will do little to nothing for performance. '
Here's the thing (and I can't comment on the sound; Youtube is good for that):
Buying a catback system by itself is going to net you MAYBE a few extra HP, IF it happens to be a fully mandrel bent exhaust with no crush bends whatsoever.
On the other hand, if you're looking for some added performance, you can pair the exhaust system with the intake resonator delete mod, and as long as you've done it correctly, the throatiness of the sound will increase along with the potential power gains.
To answer your question about 2.5" vs 2.25" pipes, I'm going to step up to my podium for a second and explain basic exhaust theory. First, anything you hear about "backpressure" aiding in exhaust flow for modern vehicles is wrong (I'm sure I'll be flamed for that statement). What people really mean when they say "backpressure" is "exhaust gas velocity." Roughly speaking, the smaller the pipe diameter, the higher the VELOCITY (think of a capping a hose with your thumb). The larger the diameter, the higher the FLOW (meaning overall exhaust gas volume).
Obviously, the goal is to be a perfect balance between the two; an ideal velocity aiding in scavenging (the movement of the exhaust gases in the piping creating a vacuum and actually pulling the fresh mixture in the cylinder), and an ideal flow allowing for large enough volume to evacuate the cylinders fully.
In terms of your current line of questioning, it seems as though a 2.5" single-exit cat-back setup would suit your needs best (no recommendations from me on brand, though). My reason for saying so is this: if you're not planning on getting a significant power increase, but just the sound, a cat-back is an acceptable setup (many people here have them, and will attest to that). 2.5" will resonate nicely in a single-exit setup.
Gaining a significant power increase (on the exhaust end of the motor only) requires replacement of the exhaust manifolds (typically with long-tube headers), the cats (since they are the next major point of restriction), the Y-Pipe (take a look at the crappy engineering in THAT one sometime), and likely some custom fabrication to boot. I'm currently putting together the parts for a custom true-dual setup with a crossover pipe and full custom center-exit exhaust tip. All items are 2.25" because going bigger would likely hurt my fuel economy.
Haven't got a chance to weld it all up, but to give you an estimate of the cost, I probably have around $1200-1300 in parts, and still have more to buy. Everything in my setup is 304 stainless, no different grades, and will be MIG welded with 308LSi wire.
Unfortunately, nothing that builds power is cheap.