Thanks for the extra info. At the moment four quaiity presets that come with DS4 meet my requirements, but as I experiment, tweeking these settings may help improve renders.

Do you know how the shading rate for the UberEnvironment relates to the overall shading rate set in the general DS Render Settings? The rate for the light (default 32) appears to be high in comparison with that in the general Render Settings (default 2.0 better at 0.2-0.5). Does one rate take precedence over the other or are they combined in some manner?