are you testing this in a packaged game or editor? if editor, check your slate with stat slate
the editor takes a tremendous amount of fps and when you have new windows open apart from your map your framerate gets very bad
i was struggling optimizing a speedtree forest with kite demo grass to test, with quite alot of trees and density - i was getting around 70-80 fps in the editor and 120 in the packaged game because the editor was taking around 7ms
granted this was on a 970, but still - hope this can help maybe