The lightest arrow isn't always the flattest shooting. An arrow is much like a bullet. For example the trajectory chart on different bullet weights for A 30-06 My chart shows that of the 150 grn, 165 grn 180 grn and 220 grn bullets, the 180 grn has the flattest trajectory and most down range KE. Unfortunately there are so many more factors in archery that there really isn't any chart to tell you what weight arrow will fly the flattest for you and your bow. Many who go with the lightest arrow possible not only are not shooting the flattest trajectory possible, but also causing more noise to boot. The lighter your arrow, the noisier they shoot and more stress you put on your bow.
Another big myth is the faster an arrow spins the more accurate. It doesn't take much spin to stabilize an arrow although some broad heads need more than others.. The more energy the arrow uses to spin, the less energy to carry down range. It's all a balancing act. Start with the correct spine and see what works best for you and your set up.