Hi,
The effect of the Mountain Erosion (as well as the effect of the other erosion nodes) heavily depends on the quad size.
It's unfortunately not possible to get the same result on a coarser terrain.
The only preview you can have is a preview on a small part of the terrain (by using a Crop node for instance).
To boost the performance of the erosion nodes, try to limit the number of iterations: the difference between 200 and 500 itérations can sometimes be subtile. You may also get the same result with fewer iterations by boosting the other parameters.
You can disable the node when you don't need it.
You can also set an Export node followed by an Import node with the same file name. For instance split your graph into 2 parts. The first part ends with an Export node. The second part starts with an Import node with the same file name. Once the first part has been computed and exported, you can work on the second part without having to recompute the first part, even if you close Instant Terra and open it again, as long as you don't need to modify the first part.
