No performance improvement from open diferential, unless your car is useing the wheel slipage as a way to multiply the tq because your tq converter is too tight. There is no tq multiplying though.

Back before my car had any musterd I swapped from a 2.94 open to a 2.94 sg both 7.25s and it felt slower with the SG but ets were quite a bit better and on the street I could finally get a jump on my wife in her maxima.