I have a similar problem, but it gets worse when reducing the field of view.
Using the settings suggested above it gets a little better, but at low fov values under 30 or so, frames still drop terribly low, which make a zoom function impossible.
It didn’t happen in the past though. So I need to figure out when it changed. But I never took close attention to that issue. It might have been related to switching from 5.2 to 5.4. But could also be some setting I changed in the course. It worked perfectly fine in the past though. Hm.
Finally realized my mistake. Some time ago I set r.RayTracing.Culling to 0 to have shadows draw further. That’s when the issues started. Now I changed that to 3 and put a large enough r.RayTracing.Culling.Radius=150000 (set to your needs).
Now it’s not updating the whole terrain anymore each time, which helps a lot! 