Recently computed terms of orders O(\alpha_s^4 n_f^2) in the
perturbative series for the tau decay rate, and similar (new) strange
quark mass corrections, are used to discuss the validity of various
optimization schemes. The results are then employed to arrive at
improved predictions for the complete terms order O(\alpha_s^4) and
O(\alpha_s^5) in the massless limit as well as for terms due to the
strange quark mass. Phenomenological implications are presented.