  Gaia benchmark stars are selected to be calibration stars for different
spectroscopic surveys. Very high-quality and homogeneous spectroscopic data for
these stars are therefore required. We collected ultrahigh-resolution ESPRESSO
spectra for 30 of the 34 Gaia benchmark stars and made them public. We quantify
the consistency of the results that are obtained with different high-, and
ultrahigh-resolution spectrographs. We also comprehensively studied the effect
of using different spectral reduction products of ESPRESSO on the final
spectroscopic results. We used ultrahigh- and high-resolution spectra obtained
with the ESPRESSO, PEPSI, and HARPS spectrographs to measure spectral line
characteristics (line depth; line width; and EW) and determined stellar
parameters and abundances for a subset of 11 Gaia benchmark stars. We used the
ARES code for automatic measurements of the spectral line parameters. Our
measurements reveal that the same individual spectral lines measured from
adjacent 2D echelle orders of ESPRESSO spectra differ slightly in line depth
and line width. When a long list of spectral lines is considered, the EW
measurements based on the 2D and 1D (the final spectral product) ESPRESSO
spectra agree very well. The EW spectral line measurements based on the
ESPRESSO, PEPSI, and HARPS spectra also agree to within a few percent. However,
we note that the lines appear deeper in the ESPRESSO spectra than in PEPSI and
HARPS. The stellar parameters derived from each spectrograph by combining the
several available spectra agree well overall. We conclude that the ESPRESSO,
PEPSI, and HARPS spectrographs can deliver spectroscopic results that are
sufficiently consistent for most of the science cases in stellar spectroscopy.
However, we found small but important differences in the performance of the
three spectrographs that can be crucial for specific science cases.
