- Use Display->Proxy Cache mode, to bake the entire RC model. It locks the RailClone object, and avoids to rebuild everything with each scene change.
It's not necessary to export it to a file. Just use the Embedded mode, which is very efficient. If you need to edit RC, just disable Proxy Cache, edit and lock it again when done.
- For objects which are the same for several houses, use "Free Object" as you pointed out, but also be sure to create a Max instance, not a copy.
In this way, internally there is a single copy of the RailClone object. It takes less space and rebuilding is faster.
- Try with different Display modes (Mesh, Point-Cloud, Quick mesh) and compare. But in this case i would suggest Quick Mesh + Proxy Cache.
- The only benefit to use XRefs is to save space in the main scene, and to keep objects in separated files. But object processing is not faster.