  Galaxy clusters are hotter and more X-ray luminous than in quiescence while
they undergo major mergers, which also transiently increase their
strong-lensing efficiency. We use semi-analytic models for both effects to
study how cluster dynamics in different dark-energy models affects the X-ray
selected cluster population and its strong-lensing optical depth. We find that
mergers increase the number of observable X-ray clusters by factors of a few
and considerably broaden their redshift distribution. Strong-lensing optical
depths are increased by a very similar amount. Quite independent of cosmology,
X-ray bright clusters above a flux limit of $10^{-13.5} \mathrm{erg s^{-1}
cm^{-2}}$ produce $\sim60%$ of the strong-lensing optical depth, and only
$\sim1%$ above a flux limit of $10^{-11.5} \mathrm{erg s^{-1} cm^{-2}}$ if
mergers are taken into account.
