  We extend an earlier study of the Landau gauge quark propagator in quenched
QCD where we used two forms of the O(a)-improved propagator with the
Sheikholeslami-Wohlert quark action. In the present study we use the
nonperturbative value for the clover coefficient c_sw and mean-field
improvement coefficients in our improved quark propagators. We compare this to
our earlier results which used the mean-field c_sw and tree-level improvement
coefficients for the propagator. We also compare three different
implementations of tree-level correction: additive, multiplicative, and hybrid.
We show that the hybrid approach is the most robust and reliable and can
successfully deal even with strong ultraviolet behavior and zero-crossing of
the lattice tree-level expression. We find good agreement between our improved
quark propagators when using the appropriate nonperturbative improvement
coefficients and hybrid tree-level correction. We also present a simple
extrapolation of the quark mass function to the chiral limit.
