I keep hearing that boo shafting is less spine sensitive than wooden shafting.  The arrows that I am working on are for a 53# longbow at 26" draw.  The bow has no cutout and the string falls right down the center of the handle.  How broad of a spine range should I be looking for?  I have 7 shafts straightend, weighed and spined.  The weights are all about equal at around 300+/- gr. The spines range from 45-55# and one is around 70#.  Thanks for any input.