There is a negligible difference in flow between OE and aftermarket converters, period. Any increases in flow are attained simply by using less substrate, and/or a smaller case. Which btw, is less effective emissions wise, and is the very reason Carsound/Magnaflow no longer lists a "high flow" converter in their catalogs any longer. There is no trick to finding the proper converter for a OBD2 vehicle that will keep the MIL off, btw.
Additionally, the construction of the substrate itself, which is the defined restriction in a catalytic converter has nothing what so ever to do with "the big green thumb". The efficiency of the converter in no way causes additional restriction to the flow of exhaust. To put this in a simple way you can understand, the wash coat applied to the substrate has no individual property which would, or does contribute to restriction of exhaust flow.
And no, this doesn't fall into the same category as "shorty vs long tube headers". Facts are facts. In this day and age manufactures are very careful regarding performance information released about their products. It has to be verifiable. If not, they could be sued by either a consumer, or a competitor, and in my 35 plus years in the business, I have seen both occur when manufactures run fast and loose with the facts. Unfortunately, I doubt you can show me a dyno sheet from any of the forums you listed that show anything more than a negligible difference between OE, and aftermarket converters regarding flow rate or HP increase. This would have to be a test where ONLY the converter(s) had been changed, and nothing else, and would have to be a legal converter. Otherwise, what is the point. Always compare apples with apples my friend.
Shoot with PB blaster every day for about 4 days and it will come off for sure.
