TFOX, Maybe this will help, KE is the amount of stored energy within the arrow. It takes more energy to propell a 400 gr. arrow to lets say 250 fps than it does to propell a 300 gr. arrow to 250 fps. The energy is stored within the arrow. Where FOC comes into play is that with an extremely heavy FOC the arrow will tend to nosedive. When the arrow begins to nose dive the fletchings will have more pressure on the air. Causing them to dig into the air. This starts to slow the arrow down. With a reduction in speed the kinetic energy will also reduce accordingly. You can get too light FOC and the arrow will loose its stearability because the fletchings aren't "digging in" the air. Thats where the FOC recommendations come from. It will give you the optimum steerability with the minimum drop. As far as wind being a factor. It takes more wind energy to blow a heavier object the same distance than it does to blow a lighter object. Thats where the heavier arrow will be more stable in the wind. I shoot alot of 3-D competitions and choose to go with a heavier arrow(423gr.), by 3-D standards. I do much of my shooting in the wind. The guys with the 350 grain arrows have alot of problems when it gets windy. I can usually get everyone of them because the wind is less factor for me. Shooting at 280 fps. I find that I can still run with them on a calm day. But in the wind I can usually pull away. Hope this helps you understand.