  The performance of two recent {\em ab initio} computational thermochemistry
schemes, W1 and W2 theory [J.M.L. Martin and G. de Oliveira, J. Chem. Phys.
111, 1843 (1999}], is assessed for an enlarged sample of thermochemical data
consisting of the ionization potentials and electron affinities in the G2-1 and
G2-2 sets, as well as the heats of formation in the G2-1 and a subset of the
G2-2 set. We find W1 theory to be several times more accurate for ionization
potentials and electron affinities than commonly used (and less expensive)
computational thermochemistry schemes such as G2, G3, and CBS-QB3: W2 theory
represents a slight improvement for electron affinities but no significant one
for ionization potentials. The use of a two-point $A+B/L^5$ rather than a
three-point $A+B/C^L$ extrapolation for the SCF component greatly enhances the
numerical stability of the W1 method for systems with slow basis set
convergence. Inclusion of first-order spin-orbit coupling is essential for
accurate ionization potentials and electron affinities involving degenerate
electronic states: inner-shell correlation is somewhat more important for
ionization potentials than for electron affinities, while scalar relativistic
effects are required for the highest accuracy. The mean deviation from
experiment for the G2-1 heats of formation is within the average experimental
uncertainty. W1 theory appears to be a valuable tool for obtaining benchmark
quality proton affinities.
