Basically, Top Tiers who are currently High 6-A or higher: At least 7-B, likely far higher.
High tiers, characters scaling to DMC1 Dante (base): At least 7-B
Characters scaling to, or around Griffon: 7-B (Including Trish. She may have hurt Dante twice, but it was made very clear she was going to get absolutely trashed in a straight up fight. And many implications in the game suggest she is likely inferior to Phantom and Nightmare considering she was shocked at the former's defeat, and fought on the side-lines for the latter).
Lady being Likely 7-B in the anime for fighting Trish, but the legitimacy of whether Trish was taking her seriously or not is questionable, as she was completely unharmed (outside of a small cut to the torso) and very casual about the whole engagement, whereas Lady was fighting in earnest.
I think Nero might need a key separation (but might be unnecessary) to yielding Yamato, and without it. He doesn't have any feats scaling to 7-B characters until after he acquires the weapon, and has only fought Low 7-B characters such as Berial, and his blade was casually caught by a base-form Agnus (
Nero visibly struggling to pull his blade back with Agnus seemingly care-free), whereas Nero low-diff'd him later in the game. So basically Low 7-B Start of game, 7-B after acquiring Yamato (obviously higher w/ DT).
Everyone else SHOULD remain the same, unless I'm missing something.