  Our recently developed variant of variationnally optimized perturbation
(OPT), in particular consistently incorporating renormalization group
properties (RGOPT), is adapted to the calculation of the QCD spectral density
of the Dirac operator and the related chiral quark condensate $\langle \bar q q
\rangle$ in the chiral limit, for $n_f=2$ and $n_f=3$ massless quarks. The
results of successive sequences of approximations at two-, three-, and
four-loop orders of this modified perturbation, exhibit a remarkable stability.
We obtain $\langle \bar q q\rangle^{1/3}_{n_f=2}(2\, {\rm GeV}) =
-(0.833-0.845) \bar\Lambda_2 $, and $ \langle\bar q q\rangle^{1/3}_{n_f=3}(2\,
{\rm GeV}) = -(0.814-0.838) \bar\Lambda_3 $ where the range spanned by the
first and second numbers (respectively four- and three-loop order results)
defines our theoretical error, and $\bar\Lambda_{n_f}$ is the basic QCD scale
in the $\overline{MS}$-scheme. We obtain a moderate suppression of the chiral
condensate when going from $n_f=2$ to $n_f=3$. We compare these results with
some other recent determinations from other nonperturbative methods (mainly
lattice and spectral sum rules).
