Originally Posted by alz0rz

well remember the point of getting rid of your stock CAT (apart from the sound) is to remove the restriction in the exhaust.

the high flow cat still has a restriction but it is much less then that of the stock CAT though they tend to burn out quicker.

the straight pipe.. is exactly that.. no restriction at all and completely free flow.

for the absolute most hp gains you'd ideally get a straight pipe but that's up to you and if you're willing to find a way to pass emissions, deal with the smell, and loudness.