Normally I don't notice these kinds of things, but maybe I'm leveling up in Artist, because I was wondering why the skybox in my level looked so pixelly and banded. It was actually made up of 1024x1024 source textures, so...why?
Turns out they default to 512 width max, and lose a lot with compression as well. Override For Standalone, 1024 Max Resolution, Format Truecolor. Much better. Still banding but I think I can live with that. But so much memory for a skybox seems extreme even in this day and age. I managed to get the memory usage down some with Texture Type Advanced, Generate Mip Maps off, Format RGB 24 bit. Still seems extreme, but maybe that's just because I'm old. (And 512x512 is probably fine for a skybox that doesn't have tiny stars...)