Seems like almost all my Mathews, have been a slight bit heavier than peak, usualy near to 4 pounds so I will get 73-74 out of a 70# . I would go 60, shoot 60, and go up or down for spine. If spine proves non-critical as I have usualy found to be the case with release, then crank it as far as you can comfortably shoot it, I would guess you wil get at least 62 out of it.