Just installed LR6 (LR CC) and converted a test catalog to LR6. The test catalog has it's "settings" stored with the catalog and these seemed to have migrated to the new catalog OK. However, several preferences didn't migrate. The primary example I noticed right away was that my view options did not migrate. After doing some sleuthing I found a "Lightroom 5 Preferences.agprefs" file in the appdata/roaming/adobe/lightroom/preferences' folder, so made a copy of it in the same folder and renamed it "Lightroom 6 preferences.agprefs". This fixed the view options problem but if someone knows of a good reason not to do this let me know.
But for the life of me I can't figure out how to get my identity plates to migrate from LR5 to LR6. Does anyone have a way to do this?