Mark, I just looked at one of Adams graphs posted at paleo Planet with a bow of similar speed per grains of arrow weight per pound of draw weight. At 4 grains per pound( 200 grains) the bow was hitting about 260, at 5.5 grains per pound ( 275 grains) the bow dropped to about 220 fps. That seems to be the break off point where lower weights really have dramatic effects on speed.