Stock manifold through converter is 2.5" and the muffler back is 2.25"

Borla catback is 2.25"

Gibson catback is 2.25"

Magnaflo catback is 2.5"

MBRP catback is 2.5"

Flowmaster catback is 2.5"

Banks catback is 2.5"

so, 2.25" or 2.5 inch. Which is "better"? I know that the larger diameter will flow better at higher RPM. I also know that my Jeep is RARELY above 3000 RPM. Rumors abound about narrower pipe and backpressure and velocity at low RPM. What is the reality of all this?