I've done back to back comparisons, same car, same engine, same tires with OEM and SD intake. SD intake and 3.91's, barely spin tires on idle stomp. OEM intake and 3.23's, much more spin from idle stomp. That's proof positive of low end difference.

This was a basically stock magnum 383 spec motor with 268H cam and 906's with normal 3 angle VJ, headers, 750 holley, nothing fancy at all.