Our renormalization group consistent variant of optimized perturbation, RGOPT, is used to calculate the nonperturbative QCD spectral density of the Dirac operator and the related chiral quark condensate $langle bar q q rangle$, for $n_f=2$ and $n_f=3$ massless quarks. Sequences of approximations at two-, three-, and four-loop orders are very stable and give $langle bar q q rangle^{1/3}_{n_f=2}(2, {rm GeV}) = -(0.833-0.845) barLambda_2 $, and $ langle bar q q rangle^{1/3}_{n_f=3}(2, {rm GeV}) = -(0.814-0.838) barLambda_3 $ where the range is our estimated theoretical error and $barLambda_{n_f}$ the basic QCD scale in the $rm bar{MS}$-scheme. We compare those results with other recent determinations (from lattice calculations and spectral sum rules).
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