Use 7z compression (lossless). The default archives are stored in a way that is not compressed. Compare the earlier Fallen Doll/Paralogue releases which used UnrealPak-ed files which instantly shrunk several hundred MB using 7z instead.
Will update with a link when done uploading to ZippyShare. Only free one I know and bother with.
Forum rules for sharing should probably be updated with "use 7z where possible" and tips such as to UnrealPak unpack games (and a tutorial on how to derive the AES encryption keys, easy) to unpack them and then compress. Great savings all around.
7z is 360MB packed, 2.4GB unpacked.