Skylight seems to be the culprit , choking up 3D spacemouse events.
With Skylight off, the movements are smooth again, ALSO in Raytraced mode !
So now i tried setting the RhinoCycles.DpiScale back to 1 - and the 3D mouse panning is super cool. I can now see the UsefastDraw effect as intended Nice !.
My MacMini is fanning up again, but not as massive as before, and no other weird stuff is happening on the other progams, I have open, writing text etc works fine.
Even scrolling through the Materials panel in Raytraced mode is smooth and nice.
Thanks a lot to @BrianJ for the tip of the Skylight !
With a simple tip like this, and perhaps some auto /on/off Skylight when panning in Rendered and Raytraced mode, I can see the new MacMini 2018 being of use for consumer level Mac owners like me, and within a reasonable pricetag. Good to know !