RE: weight vs spine
from what ive gathered by looking at the #'s at least on aluminum arrows..
is that outside diameter of the shaft has more effect on stiffening the spine than the wall thickness...
for example
a 2216 shaft has a spine of .376 weight is 348 grns
a 2018 shaft has a spine of .474 weight is 357 grns
a 2020 shaft has a spine of .426 weight is 392 grns
target shooters will shoot arrows like a 2413 because its a fatter shaft it is a stiff shaft spine .365 and its fairly light because of the thinnerwall thickness wieghing 302 grns plus they cheat the lines with there big arrows.
wall thickness (the last 2 #'s) have more effect on keeping the weight of the shaft up. but it stiffens at the same time just not as much as the diameter