From my experience and what I have read, one can expect a 5 fps difference in going from dacron to fast flight. Another few fps are possible when going from fast flight to a skinny string, i.e. fast flight with a low strand count. I have also read articles where people have measured the “noise” difference between dacron and fast flight strings. The conclusion was that fast flight really isn't any noisier than dacron. However, it is a different pitch of sound. For me, a fast flight string actually sounds quieter, because my hearing is shot at high frequencies. For someone, or an animal, with good high frequency hearing, maybe it sounds louder. I shoot fast flight on all bows that are built for it, which is all of my bows except for a few classic Bear bows more than 50 years old, and some antique bows that I don't shoot at all.