I was working around with some Settings in the ConfigOverrides.XML, because since weeks I was trying to get rid off all those Microstutters I was playing with.
So I disabled the VERTEX and INDEX BUFFERS. And guess what, the Game runs smooth and fine even with all Sliders on 5 ! NO MORE STUTTERS.

As a bad result, however, I can not use Ankor's fantastic Shadow-Mod any longer... When I use this Mod, combined with the disabled VERTEX and INDEX BUFFERS, I get these strange Ground Textures:





When I disable the Mod (by pressing the 0-Key), the Game looks normal and fine:




Well, I can live with that, but I really don't know what these Vertex and Index Buffers are doing, and why the Game runs fine when I disable them.