I read somewhere the 4000x4000 was an old Mac thing or something. The size works fine on my Windows under VirtualBox. But I've scaled them down to 2048x2048, and that seems to work well enough. I'll post the render when it's done.

I think mapping them separately makes sense. All those different maps are a bit confusing, but it's probably better in the end.

-- I'm not mad at you, just Westphalian.