Oh, beleive me I have.
Show me one SAE document that shows a performance INCREASE from backpressure or exhaust velocity increase post collector. I'll wait.
Get informed and save the world
Part of the reason my setup includes 3” cats and mids, then necks down to 2.5” catback all the way back. To keep up exhaust velocity not to maximize back pressure. Open up your exhaust too much without enough power/velocity behind it and the pressure atmospheric becomes more than that in the exhaust, cause the air to take the path of least resistance i.e. back pressure no bueno