Hi sonstiger,
Most of the time the far away trees are being displayed as either Billboards or Impostors - both of which are using 2D images of the mesh rather than the actual mesh. They’re so much faster it does pay to use them when you can.
To get both speed and better looking far trees you can use a program such as rdLODtools (it’s on the marketplace) to create your own custom far LODs and tweak the colors and sub-surface amounts yourself to fit in with your scenes.
It also has tools to create Single Triangle LODs - about as fast as you can get - perfect for far away trees.
Once you’ve created the Billboard/Triangle etc it’s also possible to remove all other LODs - leaving just the high speed LOD as the only mesh.