  We present three new Chandra X-ray epochs along with new ground-based
optical-UV observations as the third installment in a time-series analysis of
four high-redshift ($z\sim4.1-4.4$) radio-quiet quasars (RQQs). In total, we
present nine epochs for these sources with rest-frame temporal baselines of
$\sim1300-2000$ days. We utilize the X-ray data to determine basic variability
properties, as well as produce mean spectra and stacked images based on
effective exposure times of $\sim40-70$ ks per source. We perform time-series
analyses in the soft and hard bands, separately, and compare variability
properties to those of sources at lower redshifts and luminosities. The
magnitude of X-ray variability of our sources remains consistent with or lower
than that of similar sources at lower redshifts, in agreement with the
variability-luminosity anti-correlation. The mean power-law photon indices in
the stacked Chandra spectra of our sources are consistent with the values
measured from their archival XMM-Newton spectra separated by about three years
in the rest frame. Along with the X-ray observations we provide
near-simultaneous optical monitoring of the sources in the optical-UV regime.
The overall variability in the optical-to-X-ray spectral slope is consistent
with sources at lower redshifts and the optical-UV observations display mild
variability on monthly timescales.
