The textures in the core pack are HD, the separate pack is Ultra HD.
Not all HD environment textures have Ultra HD versions, so you will need to keep your environment folder from the core pack and copy the environment folder from the Ultra HD pack and merge folders and overwrite the default HD textures.
Edit:
There are also mipmap textures, which are basically support textures that are smaller duplicate versions of the main texture. These textures are used when you're "far away" from whatever environment texture you're looking at. So just because you have multiple "copies" of the same texture, you will need them if they have mip1, mip2, mip3... at the end of the filename.
It's also worth nothing that since the Ultra HD pack has larger resolution files, they will also have more mipmaps. So in the case where someone wants to go from Ultra HD back to the standard HD, you would have to delete the Environment folder and unzip your Environment folder from the core pack back into your SX4E01 folder otherwise you'll have extra mips sitting around.
Edit:
More mechon stuff, more big pictures. Once again, not actual retextures but just cleaning up the edges. Feathering and removing a few pixels along the edge. I'm not sure if this stuff will end up in the pack or if it will just be a side pack. It looks wayyyyy better imo, but it's not really HD.
Metal Face
Another Mechon
Not all HD environment textures have Ultra HD versions, so you will need to keep your environment folder from the core pack and copy the environment folder from the Ultra HD pack and merge folders and overwrite the default HD textures.
Edit:
There are also mipmap textures, which are basically support textures that are smaller duplicate versions of the main texture. These textures are used when you're "far away" from whatever environment texture you're looking at. So just because you have multiple "copies" of the same texture, you will need them if they have mip1, mip2, mip3... at the end of the filename.
It's also worth nothing that since the Ultra HD pack has larger resolution files, they will also have more mipmaps. So in the case where someone wants to go from Ultra HD back to the standard HD, you would have to delete the Environment folder and unzip your Environment folder from the core pack back into your SX4E01 folder otherwise you'll have extra mips sitting around.
Edit:
More mechon stuff, more big pictures. Once again, not actual retextures but just cleaning up the edges. Feathering and removing a few pixels along the edge. I'm not sure if this stuff will end up in the pack or if it will just be a side pack. It looks wayyyyy better imo, but it's not really HD.
Metal Face
Spoiler:
Spoiler: