I should have been more clear with my statement. What I was trying to convey was: A MagnaFlow cat purchased in Nevada, Florida, Texas (where ever) performs the same as a MagnaFlow cat purchased in California.....the only difference is the CARB stamp on the cat and the tax $$$ in California. I know OEM is the best way to go. But $$$ is not permitting at this time. As for the percentages of efficiency......I don't know. I do know that last year I purchased a 'direct fit' cat for my other daughters 2004 Volkswagen Passat (v6). The brand was also MagnaFlow.......with the CARB stamp/tax on it. I bought it thru a local Autozone parts store. The price was $760 I installed it, cleared the cat related code, drove it while I had my laptop connected to the car, watching the emissions monitors...........as soon as all monitors had 'readied', I went to the smog shop for inspection and the car failed due to tail pipe emissions........Visual and Functional passed.......just burned dirty......Brand new cat burning dirty.........so I borrow a 10 year old cat off my neighbors VW Passat and run the smog test again......it passed. Some cars just run closed to the max allowable emissions.