Like Pat says... there are many other factors especially with a warbow.
From the little experience I have, I'd guess most warbow shafts are over spined, but if you have the very heavy head and big fletchings you can get away with it. It's all down to what you want from the projectile maximum impact energy, maximum range or maximum accuracy.
Flight shooting my 100# Elm, I found a 5/16" 40-45 spine arrow flew best... that would seem ludicrously under spined, but there was very little head weight to keep the front going straight and to provide the inertia against which to flex, not much fletch to straighten it up either.
Del