For years many independent testing facilities have measured and publishedefficiency data on bows shooting an array of arrows from very light to very heavy.Data is available on litereally hundreds of bows from recurves to the most exotic of cam designs. You can go to the news stand any time and pick up a copy of Bowhunter magazine who publishes such data every month. In not one single case on literally thousands of measurements has efficiency been shown to fall back when arrow mass increased. In every every single case efficiency and ke increased as arrow mass increased. There is no sweet spot regarding arrow mass and ke. As you go lighter and lighter the bow shoots the arrow less and less efficiently wasting more and more energy in vibration and noise. This effect will continue to worsen as you go lighter and lighter all the way down to dry firing the bow.