Forest create rules for big landscapes

Hello everyone.
I create landscape 4033x4033 size. And I want to create forest for this size of landscape. I tryed procedural foliage type to create but spend a lot of time to create forest that left me 40 FPS. So does anybody know rules how to create forest more realistic with big space of tree.

  1. What is better triangles size on trees for create forest?
  2. What is optimal cull distance to show forest?
  3. What is better for performance ballance of properties in procedural foliage tool?

I ask people that has experience with forest creating for their guides. Maybe you can share our solutions.

NIce one thank for sharing this, I will go ahead and check out what are my thoughts.