It's definitely in a category of its own, nothing like regular Super Saiyan nor like a potential unlock, as it gives you a completely different type of ki. Super Saiyan does seem to have its own unique type of ki, or ki signature, but it's not fundamentally different from regular ki.
My best theory is that the Saiyan's ki gets converted into God ki, 1:1. I suppose what follows is that a certain amount of God ki gives a greater battle power than the same amount of regular ki.