More important than speed increase, which will be only a couple fps, the feel of the shot will be drastically improved. A low stretch string will give you a crisper release without the "springy" feel of dacron. Less vibration and more energy transfered to he arrow. Honestly, even if there was NO speed increase, I would still use low stretch on all but a couple old irreplaceable bows. Not that I'm convinced that it can hurt them, just not taking any chances. As far as brace height, I've always found most bows to behave better at the high end of the recommended range, but that's just me.