I am a petite woman (62 inches/105 lbs) and have a 2+ year Swift V backpack, with the vest shoulder harness. I’ve used this pack two years hiking, and this year on 300+ miles of the AZT, the rigid piping on the chest became too painful with extra water weight. So, I order the S-curve shoulder harness and just completed 181 miles on the Colorado Trail. The new shoulder harness is a big improvement in comfort without the rigid piping. It is also less weight. I never found a good use for the zippered pockets on the vest and always left them empty. The S-curve harness also allows much more ventilation to my back, increasing the comfort level in hot weather.
A couple negatives: The pockets on the shoulders are too narrow on the bottom (they taper). I carry a 3 oz tube of sunscreen in one pocket and it barely fit without showing. The pockets could also be sewn lower or made adjustable. If I was carrying a small .7 water bottle in the shoulder pocket it would be in my face. I instead carry 1 Liter bottles in the side pockets.
A second minor negative is the chest strap on the harness. The sewn loop blocks the tightening of the elastic chest strap by 1.5 inches. As a small women, I would welcome that extra length for tightening the chest strap when traversing slopes. I am evaluating whether to adjust the position of the seam.
Overall, I recommend the S-curve harness over the vest harness.