SO i have similar with my index / 2070super. Things that help: 80hz no motion smoothing. MSAA is the FPS killer but that and shadows make things look really nice so it is a balance. I have tried reducing number of cars but that didnt change much so its mostly as balance of how low can you cope across the settings. I found reducing the resolution helped a bit so I run at 96%, the index is good enough IMHO that you can get away with (whatever the reverse of super sampling is).