When I had my exhaust done at carline the mechanic told me that my car came out originally (TJ 2000 exec.) with a pretty good exhaust , and that I shouldn't bother with replacing it apart from the muffler, cat and obviously the headers. I've had all this done bar the headers (when I'm in a better financial situation). Is it worth getting the whole exhaust replaced for better performance or is this as good as it will get?

He's pretty much right. Replace the rear muffler, fit some headers, and you've made 95% of the gain you're ever going to unless you're going wild with the motor. Some have gone for high-flow cats and replaced the rest of the 2.25" piping with 2.5 or even 3", but it won't gain you much unless you're anticipating *serious* horsepower.

3.5l piping is 60.5mm i.e. almost 2.5' so going to 2.5 is a waste of time and money unless there's gains to be made from a more direct path which won't be much anyway. 3' has been proven not to be overkill even on a moderatly modified Magna.

Just go headers and muffler for the time being.

Stock is 2.25" internal with a volume of 25.66cm2

Upto to 2.5" internal give a volume of 31.68cm2. Thats a 23% increase in flow volume. I have 3" from the cat back (volume 45.6cm2 near double stock volume) and I noticed torque increased and is more useable. Bit of drone so get 2 x resonators installed. Should cost $400 max installed. I got the Berklee PEX 2.5 muffler. So not a *proper* 3" cat back. But I am running a twin 2.5" muffler setup when the turbo goes in so it's all relavant then.