Right every1 calm down!! imnot4n, if you tell other ppl not to leave ignorant posts then why do it yourself? surely then your just as bad as them!!
Anyway, back to the thing wer all here 4, CAR TALK!!
If you have a 2 inch inlet and outlet from your hi-flow cat you have to options-
1*Ditch the cat and put a de-cat pipe in, your header will be 2.25(or 2.1!! cant remember), so theres no point in a 2 inch cat restricting it. I'd get a de-cat and a cat back exhaust with 2.25 piping so no flow is restricted. Just make sure you geta good quality mandlel bent one.
2*If you want to keep your cat, any cat back exhaust of 2 inch or upwards should be fine, coz only so much gas's can get through the cat anyway.
As for sound, as every1's already said each to the own, it completly depends on your taste. I have a full mongoose system inc de-cat, and just love it!!
Hope this helps, if i'm wrong bout anything any1 feel free to correct me!!