Towards improving fps, I ran some experiments...
The first low fps section is the first turn. This is borderline on whether the fps are in need of improvement. Turning shadows off helped significantly, so I'd recommend reducing the number of shadow-casters.
The second low fps section is along the river through the tunnel of trees. Surprisingly, turning shadows off did not help significantly, so I'm sorry to say that your best course of action is probably reducing the number of objects and/or texture sizes. Maybe only use a single plane for the trees in the 3rd row? Setting LODs might also pick up the pace.
Third spot is after the hairpin, after the houses, but before the road junction. Again, turning shadows off did not help significantly. This section surprises me as to why it shows a significant drop because there doesn't really seem to be more material in view than other sections.
Overall, I was surprised at how little turning shadows off helped fps on my rig. In general, it was only in the neighborhood of 10-15%.