when shooting for score fat arrows rule, it matters little if you choose carbon, aluminum or a composite , aluminum can bend so can composite carbon can not bend, but it can break, fiberglass is super heavy and not popular... keep the weight to a minimum of 5 grains per pound of draw weight,, 60# =300 gr arrow, 70# = 350 gr arrow,,, spine is the stiffness of the shaft, it needs to be matched to the length of the shafts and the weight of the bow,,, there are charts and programs that can tell you what spine is needed,,, too soft or too stiff accuracy suffers, to soft can also be dangerous to shoot, when in doubt about spine always go stiffer if it is close( commonly refered to as being on the bubble, kinda like standing on the fence, you could fall either way) being a little stiff usually causes no problems,, but you do not want a 200 spine arrow when you need a 400 spine,,, spine is determined by flex of the arrow at a specfic weight and length