I use.004 - .005 and tapper from 1.25 to .35 - .40 at the tips, depending on the desired weight, on a moderate R/D longbow. Remember, you can take off approximately a 4 to 1 ratio of the width compared to the depth and maintain the same weight; the narrower the tip, and more importantly the limb, the less mass. However, speed isn't everything, ultimately it comes down to the "FEEL" of the bow when an arrow is released. In the words of Tim Lott, dead is dead, the animal doesn't care much. I'm still experimenting with the ratios to find what's right for the profile of my R/D's. Your ratios will differ, dependent on the stack, width, Taper, and materials used. Lots of variables to account for.