  The Bjorken sum rule and R ratio are constructed to $O(a^4)$ in the Landau
gauge in the three momentum subtraction schemes of Celmaster and Gonsalves
where $a$ $=$ $g^2/(16\pi^2)$. We aim to examine the issue of convergence for
observables in the various schemes as well as to test ideas on whether using
the discrepancy in different scheme values is a viable and more quantum field
theoretic alternative to current ways of estimating the theory error on a
measureable.
