Difference: HKS (silly money second hand), or gutted stock CAT: more top end power,=20 gets rid of that 5-5.5k tail off. But both look standard so nobody=20 suspects, using a HKS is slightly healthier for your lungs, and a lot=20 less messy than gutting the cat.
Full decat/downpipe: spools up at lower revs, gives a slight increase in=20 torque lower down, gives the same top end increase as HKS/gutted.
Both will give a slight increase in noise, the full downpipe will be=20 slightly deeper in tone.
Gutted CATS normally sell for about =A340-60 on Ebay.
--=20 "Sorry Sir, the meatballs are Orf" The poster formerly known as Skodapilot.