I am also having the Witcher 3 terrain rendering issue. It seems like the terrain is rendered at a different distance than objects on the terrain. There is also a similar problem with the graffiti on the walls at the inn at the start of the game. The graffiti seems to kind of float on the wall. I am using a fresh install of GOTY edition. Issue persists on Ultra and Low quality. I’m using a 1080 ti and HTC Vive.
I have a lot of mods on my Skyrim, so there’s no need to troubleshoot me. I’m just saying that every time I have a game that stutters or has low fps, my CPU is always at 100. So that may be the issue for OP.
You probably have a CPU bottleneck. I have the same issue with my 1080ti and my i5-3570k CPU (I’m upgrading it soon). Open task manager and see if your CPU is at 99 or 100 when the game is running. VR and Vorpx take a good chunk of CPU, so does Skyrim. The only thing you can do is try to disable effects that use more CPU like particles and shadows.