My mistake. You're correct, the master program including unfinished levels is something like 10Tb and Rage was made from about 1Tb of that. However, you need an industrial computer to run that. The 150gb is, I believe, the least compressed version that will run on a desktop and Carmack hinted they might be releasing a 75gb texture pack.
The real mystery is how much vram you need to run that and how much of an improvement it provides. The Megatextures are huge and have to reside somewhere, but most graphics cards only have enough vram for Dx style games that use smaller textures. The thought of how much memory will be required to add ray traced geometry to the engine in the future is mind boggling. Still, its pretty obvious if people really want to move beyond Crysis style graphics and take it to the next level something like this required where sheer bandwidth and putting all those thousands of processors on a computer to work is the only way to go.
