My only suggestion would be to delete the UI and Prefs and any other subdirectoys under runtime for P4 that doesn't include model information. Even Python, I'd move Python to the P6 directory as it only runs Python scripts from within it's main runtime, or so I was told. In otherwords,

Runtime: Geometries
                  Librairies
                  Lights
                  Reflection Maps
                  Templates
                  Textures

Are the ones you really need to keep, plus any downloaded content directories with INJection information like all those DAZ subdirectories that start with the ! Mark.