Okay, some test results:
Super Mario 3D world (US) - unpacked .Wud with Uwizard, then compressed it with 7-zip / WinRAR
Wud: 25,025,314,816 bytes
Wux: 2,804,613,120 bytes
.7z (Ultra): 1,097,111,768 bytes
.rar (RAR5): 1,416,623,273 bytes
.tar.gz: 1,465,158,477 bytes (7-zip...