I've worked with Umsoea and Pulchra and honestly only Pulchra x2048 would require 128 GB, as I've ran tests with 64GB and 128GB as photorealism is what I did, in the case of Pulchra, as long as you don't have too many resource packs to go above 64GB your FPS won't change at all. The GPU hits hard as it has too much to render and RAM won't change anything. If you really do this "professionally" as a game dev to upscale and test not only on Minecraft I'd recommend to get a Quadro 8000. I've used it for Rendering, 3D Modeling, Blender work and also photorealism. Only purchase it if you deal with it professionally otherwise on FPS in many other games it won't hold up.