For a new class of ship, I would think Starfleet would probably have a more even-numbered registry. Something like NX-400: USS Bonaventure.
As for suggestions, i'd say something like:
NX-400 / NCC-400: USS Bonaventure
NX-400 / NCC-400: ISS Mussolini (mirror Bonaventure)
NCC-452: USS Leonardo da Vinci / USS Leonardo / USS da Vinci
Not sure what to name the 3rd ship, but I figured Leonardo da Vinci would be a good choice since he has appeared a few times in Star Trek, and fits into keeping the ship names based on famous Italian people. I used the number NCC-452, since da Vinci was born in 1452. I figure Benito Mussolini would be a good choice for a mirror universe Bonaventure, since a dictator would be pretty much completely opposite of sainthood.
Although I suppose in a universe where good people are bad, and bad people can either be good, or worse. Maybe Saint Bonaventure, wasn't really a saint, and Mussolini might've been a good guy