Usually C60 are thicker than C90 tapes, so they can handle a little more signal before saturation.
Also cassette decks recording calibration and rec/play performance measurements are performed with C60 cassettes.
A cool website for those who like cassette tapes collecting :
https://www.tapes.fans/
They even have a page for the Phoenix cassettes :
https://www.tapes.fans/catalog/category/compact-cassette/phoenix
I have some Ampex/Quantegy 472 cassettes from Opelika AL and from Peachtree City GA, great type II tapes.
The Opelika one has a That's Suono style shell :
The Peachtree City one which looks like a black Sony Metal Master but in plastic instead of ceramic :