Going back to my comment I made earlier, I was wondering if there was enough evidence in this to propose an upgrade thread for Raava and Vaatu when they are at their full power?
Korra in Book 4 uses the spirit vines to find where people are in Republic City by helping her lock on to their spiritual energy, and later uses them to see what's going on in the swamp despite the swamp being hundreds of miles away. Toph states that she can see everyone on the planet using the spirit vines, which are invisible in the ground until they're lit up by spirit energy. She states she even used them to see what was going on in the South Pole during the Civil War, so these pathways even cross through the ocean.
In the season 2 finale after he has temporarily destroyed Raava, Vaatu starts infesting Republic City with these vines, which, as already stated, has a symbiotic connection to the invisible pathways that run along the planet. Later in the series, it's shown that spirits are naturally attracted to the spirit vines and linger around them. All of this combined with Raava's statements in "Beginnings" (that Vaatu was going to "destroy the world as you know it. Darkness will cover the Earth for 10,000 years" and "Thanks to you, this world may cease to exist") it's clear that Vaatu was going to cover the entire planet in spirit vines so that dark spirits would be free to roam across the Earth. And since dark spirits can also exist in the oceans as seen by the leviathan that attacked Korra, plus the fact the Toph could see across the ocean, this applies to the whole planet, not just the landmasses. So I think that Raava and Vaatu at the height of their power should be 5-B.
Obviously if I decide to make a crt, I'll provide the actual scans. Too lazy to do so right now.