Well i have a CG modded mani and at the moment access to a CG cat, CG decat, CGA decat, and CGA cat, running into a PL/sportex system. I am not an engineer but from what i can gather, a bigger longer decat after the mani, than standard, would increase the venturi effect as more gas could build up and then draw at higher pressure, this would be benificial at higher rpm as the flow rate would be quite high and draw more gas out. At low rpm i can see this causing a stalling effect in the exhaust gas flow tho, but i can deal with this, maybe i am shooting at stars, but until i try it i dont know