That’s a good question.
The ‘virtualtextures’ folder in RAGE is a bit over 11GB, with another 6GB or so for the multiplayer textures, leaving around 4GB for the rest of the game data (overall install size is 21.1GB ).
A 24-bit 16384x16384 PNG filled with random coloured noise takes around 400MB (saved with Paint.NET - it was using a bit over 3GB of RAM and parts of the interface were corrupted and flickering :fffuuu: ).