This game has extreme framerate drops when 'Extra Details' and (especially!!!) 'Grass' are enabled. I get 60fps most of the time, but there are a lot of places on Myst Island where the framerate drops to 30-45 fps. No matter the resolution. Even on 720p!!! In any case, my GPU utilization never goes higher than 60% (on a GTX 970)
So, it must be of some sort of CPU bottleneck. But the strange thing is, my four CPU cores are nowhere near 100% stressed. More like three of them at 50% and the fourth at 70%. Is this some Unity engine strangeness, or is there something wrong with the Grass setting?