Yes removing a Cat, or "gutting" one is actually quite the offense, a $2000 dollar fine and a felony(which is stupid) where I am. Not that many people would ever notice that your missing one... but thats your choice, an exhaust shop might do it under the table tho if thats the way you want to go. Depends on the shop, probably have more luck with a smaller shop. It will free up a few ponies without it and sound better, and you'll get that old muscle car smell. But its also illegal.
A cat-back exhaust is simply that, its the exhaust from the catalytic converter back to the rear of the car, the tips. Does not include Headers, Y-Pipe, or a Catalytic Converter. Thats where any combonation would come in. You could get maybe some Mac or Pacesetter headers, an offroad Y-Pipe, and if you do plan on using a Cat, a magnaflow high-flo. But none of that is really needed aftermarket for a V6 unless you really plan on modding it out or maybe just want it to sound like a V8. There are some fast V6's out there, and some heavily modded ones too, but generally you don't see too many of them. So it depends on what exactly you want this car to do.
I'd just get the High-flow cat and cat-back system from magnaflow for that car unless your really planning on modding it out and racing, then like I said you may want to look into headers and such for more HP.

 

I will have my car paid off in just 8 more payments when I get it paid off I do plan on using the money I was using for payments to make it as alot faster. I have 100,000 miles on it now so I was figuring I would either have the motor rebuilt and add a super charger or just do a ls1 swap not really sure. But either way I do plan on doing alot of engine mods to increase my hp I would like to get it to about 350 or 400 hp. I know that will cost alot of money to get it that fast I just plan on taking my time and doing what I can when I have extra money. So in that case from what everyone is saying I should probably go with the 3" exhaust system right?

 

Well, if you are planning on pushing 400 horsepower, you may end up wanting more than a single 3".

My car makes approx. 350 hp and 440 tq, and I'm prolly gonna go with a 3.5" Mufflex cat-back. That would be way overkill for anything besides a HEAVILY modded 3.8 though....

- Justin

 

I wont have anywhere near that for a long time so I guess im just gonna go with a magnaflow muffler no cat and a 3" system for now thanks for everyones help and when I get it dont ill let everyone know how it went.

 

Good luck finding a shop that will remove the cat --- there may be a separate law that says shops can't remove them (West Coast Customs got gigged for taking airbags out of some of their cars). I think the power add will be negligible and not worth the trouble.

And I wouldn't trade my Borla 3" exhaust for anything.