Some notes on Load Screens which are part of the GUI.
The texture the models uses are prefixed ls_ and are usually .TGA (can be any texture but this retains the maximum quality, eg: DDS files will use the non-downgraded non-mipmapped version).
See loadscreens.2da for how to just simply add additional load screen textures the toolset/game reads. It would be recommended to use DDS for high quality client files, but TGA for the toolset (although the small file, unused by the game, can be safely left as TGA regardless).
Hardcoded Load Screens
The default hardcoded load screens are for Save and Load can be replaced;
They're the same size as usual large load screens - the smaller version is not needed since it is not toolset selectable.