Over enemy giant airfield and town at field 88, framerate going from over 60 to 20ish. I've got almost all details turned down/off except ground detail is maxed, bump mapping, and other plane skins. Everything else is off. Video mem usage is ~550mb with an R9 380.
Under any other conditions, I have had no issues with framerate that I have noticed. Even in FSO with a big bomber group.
Many other reports of people with the same issue in the area. Widely varying machine specs. One person with a high end rig and 144hz monitor had it drop to ~60-70.
Wiley.