For me there was no difference. I did some 0-60 times using a Dragy timer with standard exhausts without the front baffle and then G56 exhausts and I wasn't able to improve the time.
This was with standard cams and a free flow air filter.
Having said that, they have to flow better than the standard exhausts even without the front baffle and maybe there would be a difference if you compared them on a car without the cats and or stage 2 cams to take advantage of this.
