So Ive decided that openelec is no better than OSMC, so Im coming back to OSMC. (was trying to resolve some speed issues but OE is no faster)
So can I back up my current OpenElec config, and restore it under OSMC? (using the backup and restore functions I would assume)
Sure, why not.
At your own risk, of course.
It depends on what you are looking to restore. I do not recommend just copying over the databases. Better to export the .nfo and artwork to the media storage folders, and then import into the new Kodi.
Some addons may break between installs, it depends on each version, but the userdata/addon_data folder would probably be fine to copy. sources.xml and advancedsettings.xml should work for both installs. But guisettings.xml potentially may not. In any case, you need to have kodi shut down in order to copy it over.