That’s awesome! Adding more mountains/cliffs to remove some overdraw is something I’ve been looking into. That’s definitely a pro tip [GG]. It’s finding that balance to capture your original idea plus performance that’s really challenging. You’ve done this extremely well it seems! Your scene is stunning! 
For me, this boiled down to configuring nanite and lumen systems through CVAR’s. I also ended up altering some elements of the engine to allow me to utilize nanite more efficiently with RVT’s and landscape splines. And then optimizing any materials that were taking a long time in the nanite rasterizer.
GOOD! I DID MY JOB LOL! 
I originally matched IRL colors but found it boring. I just find general realism boring period. I love the more stylized look of the colors. But I do understand what you’re saying and hope to clean it up more. A clean stylized/realism is what I’m aiming for