The R.G. Mechanics version of World at War typically compresses the game down to around 4.8 GB , a significant reduction from the original size.
That's interesting, considering even the download is 6.5 GB. Installed size on disk should be that 9350 MB ~ 9.13GB. Steam Community Call-of-Duty -World-at-War-Repack-By-R-G-Mechanics