I have a M30 from 1992, it sounds great. However, my guess is that its not a big step up from a M20.
1963 - José Ramirez (A.M, Antonio Martinez)
1964 - Masaru Kohno No.7 (Kono)
1989 - Antonio Marin Montero (Bouchet)
2017 - Tobias Braun (Santos Hernández, 1924)
Feel free to ask me anything about Japanese classical guitars.