Style chooser

I had some questions here, I heard from most exhaust shop, which tell me auto car must maintain certain level back pressure(flow velocity).
But some says auto tranny need as much back pressure as possible to get the best fc and pick up:hmmmm:??

My current exhaust set up was
4-2-1 - 1.6(piping) - 2.0 inlet straight flow long type muffler - 1.75 straight flow ( hotbits ).

The reason I using straight flow, because when I was asking the open pod method with speedwork, they ask me to do...