I also have a GTX1080 / WMR combo (Samsung WMR), try these settings:
- Texture: ultra
- Terrain mesh: high
- Terrain image: high
- Shadow: medium
- Building: low
- Tree: low
- VR render scale: 1.50
Also, turn cumulus cloud density off / low - it's okay to use some cirrus cloud density (25%) at high altitude (75%)