No matter what I was trying, I couldn't get the environment to render in a reasonable amount of time. MentalRay died. Vray did a bit better, but couldn't handle the textures, even when they were multi level mip map exrs.
Bit the bullet and started this workflow: Combine existing rocks into clusters. Regenerate seamless mesh in topogun. Generate a subdiv in topogun. Create new UV's for the section. Repaint rock textures in mudbox. Export 30k-100k meshes for direct rendering. Getting a SERIOUS speed and memory boost by avoiding subdivs and dynamic tessalation. The memory footprint for the geometry is only 130mb now.
Need to tweak dirt shader, it's too intense, and the grass placement needs some work, but finaly there. Moving on to the wide shot. Cringe!
But the render time is only 5mins. Very doable. Will quadruple with characters and HD. But still in the realm of possibility.
There is a tiled normal map mixed in there and some procedurals to keep it working for the closeups. That way we don't have to swap out maps and have several different versions of the scene.