  Substantial effort has been devoted in determining the ideal proxy for
quantifying the morphology of the hot intracluster medium in clusters of
galaxies. These proxies, based on X-ray emission, typically require expensive,
high-quality X-ray observations making them difficult to apply to large surveys
of groups and clusters. Here, we compare optical relaxation proxies with X-ray
asymmetries and centroid shifts for a sample of SDSS clusters with
high-quality, archival X-ray data from Chandra and XMM-Newton. The three
optical relaxation measures considered are: the shape of the member-galaxy
projected velocity distribution -- measured by the Anderson-Darling (AD)
statistic, the stellar mass gap between the most-massive and
second-most-massive cluster galaxy, and the offset between the most-massive
galaxy (MMG) position and the luminosity-weighted cluster centre. The AD
statistic and stellar mass gap correlate significantly with X-ray relaxation
proxies, with the AD statistic being the stronger correlator. Conversely, we
find no evidence for a correlation between X-ray asymmetry or centroid shift
and the MMG offset. High-mass clusters ($M_\mathrm{halo} >
10^{14.5}\,\mathrm{M_\odot}$) in this sample have X-ray asymmetries, centroid
shifts, and Anderson-Darling statistics which are systematically larger than
for low-mass systems. Finally, considering the dichotomy of Gaussian and
non-Gaussian clusters (measured by the AD test), we show that the probability
of being a non-Gaussian cluster correlates significantly with X-ray asymmetry
but only shows a marginal correlation with centroid shift. These results
confirm the shape of the radial velocity distribution as a useful proxy for
cluster relaxation, which can then be applied to large redshift surveys lacking
extensive X-ray coverage.
