I totally agree that a high flow cat will in fact flow more than a stock cat.

I totally agree that when the stock cat gets clogged up with soot (which it does) then it's time for it to go, and a high-flow unit is cheaper than a stock replacement.

I totally agree that an ITR motor, or GSR motor that has been upgraded to at least ITR specs, will benefit from a high flow cat.

I totally agree that when an exhaust system is upgraded to 2.5" the cat should be as well, and high flow is the way to go.

BUT...

The plain and simple fact is that a GSR with a bolt-on intake, header and exhaust (and a non-clogged stock cat) will put about 155 hp to the wheel. Adding a high flow cat to the mix will produce...surprise surprise, about 155 hp to the wheel. You can debate the flow numbers till you're blue in the face but it doesn't change that fact.