We compute the renormalization mismatch displayed in 1-loop approximat
ion by classically equivalent 4-quark operators and coming from differ
ent possible definitions of the gamma5 matrix in dimensional regulariz
ation. The result is then employed to study the effect of the various
treatments of gamma5 upon the size of radiative corrections to 4-quark
condensates in the QCD sum rules for rho and A1 mesons. We find that
a fully anticommuting gamma5 which automatically respects non-anomalou
s chiral Ward-Slavnov identities leads to considerably smaller correct
ions and reduces theoretical uncertainty in the QCD prediction for the
tau hadronic decay rate.