Hey,
after resizeing my landscape the FPS gain was very too little. I only gained 2 FPS. It got even worse in some other areas losing around 4 to 5 FPS. On top of that I would had to re-paint my landscape.
I am going to look further into my foliage, especially rocks. Lets see if there culling distance is set too high or sth.
here´s a link showing stats in UE4.
sincerely