Analysis of the Japanese FFXIII Blu-ray reveals that the game uses 38GB/50GB (DL-BD).
8GB is game data while the remaining 30GB are the CGI, in-game cut scenes, and stunning soundtrack. A few month ago Square Enix revealed they were aiming for 3DVD’s (25,5GB) on Xbox360. This essentially means, and was confirmed a few weeks ago, that 13GB would need to be compressed in order to get it running on Xbox360.
Square Enix continues to state that the Xbox360 version wouldn’t lose quality, however, we will only know for sure after viewing endless comparisons when the game hits Western store shelves on March 9th, 2010.
Former Final Fantasy storywriter Hironobu Sakaguchi had the same problems with Lost Odyssey, but it turned out to be a highly enjoyable RPG on Xbox 360.
Source: FOK! Games (Dutch)