Terrain trees or not terrain trees!!

Ok age old question I'm guessing but I will ask anyway.

I am creating a world which requires plenty of trees as you would expect. I require the trees to be harvestable which I am confident in a code format to do so both on terrain trees and tree game objects.

The problem I have is that the scripts involved in using terrain tree click and harvesting are not the greatest and can consume vital processing time using raycasts, positional detection and height detection (due to trees and their colliders being merged with terrain).

So casting that option aside I have 2 options:

1. Use totally game object trees,

2. Use a mix of terrain and game object trees where only the game object trees are harvestable.

Has anyone got any real experience to how much performance is lost using a lot of game world trees? Is there a way to use a custom LOD script so that the gameobject trees are optimized. Guess the colliders would also have an impact??

Any input would be gratefully appreciated.

Thanks

Stewart