Sounds about right, flow-wise. Unsure how much an 8k might be worth over a 4k, or at all.
As far as materials and nanite, the depth-render they run allows them to render all pixels of a single material in one-pass, there is no pixel-to-pixel switching. You DO still have to render the same amount of pixels but it’s in a batch now, which is (almost always) more performant. Nifty little side-effect of their ‘adjustments’ to the rendering process. Unsure if this property applies to nanite-meshes only or the entire scene.