first stage of doing the exhaust i got the muffler replaced with a 2.5" almost straight through muffler. boost went up 3 psi and it was certainly quicker.
looking at the stock muffler it necks right down just before the muffler, one big bottle neck.
theres actually not a huge difference in just changing the whole exhaust. the muffler change makes more of a difference than doing the rest of the exhaust.
however doing the whole exhaust means you can do other performance mods.
also you guys are lucky there is so many off the shelf kits you can get delivered and fit yourself. for me its custom build only so your paying a lot for labour.
i've gone 2.5" as i have to keep it fairly quiet for work.
only problem with 3" is its a bit tight and can sometimes hit when the motor rocks. it has to be just in the right place to clear everything.