Best Class for Massive meshes at runtime?

What is the best performing method to import and work with large meshes at runtime?

Is procedural mesh the best option at present?

We are new to UE and working on some design / simulation software for which massive (can be areas in the 10’s of kilometres) user supplied .xyz survey scan data and potentially photogrammetry assets are commonplace.

It would be absolutely magic if we could utilise nanite at runtime - is this a possibility?