Just wanted to share what worked for me (i7-6700/2080ti) with the SteamVR version of the game on a Vive Pro. The two biggest factors were setting resolution scaling to 100% and turning off Legacy Reprojection under Dirt Rally 2.0 VR settings in SteamVR.
Then, in game, set MSAAx8/Anisotropic Filtering x16, ultra preset, then turn off Screen Space Reflections and vehicle details low (everything else is maxed out). With legacy reprojection on, I basically couldn't get past the "low" preset without massive stuttering.
