Image quality of the 645Z + Pentax 90mm f/2.8 is sensational, which translates to very high per-pixel quality, minimal artifacts, consistent color, ultra low noise and high resolution.
I set up this eclectic scene, including a variety of challenging items for any camera to record faithfully. In my review of the Pentax 645Z:
This series should yield a really good sense of just how good the 645Z really is.
Includes the usual HD and UltraHD entire-frame images along with many crops and commentary.