I know it's not the same coin, but, check out the no fuss approach to G-VG grading with specific rim and letter references, dating back to 1994... John Feigenbaum, 1994, The Complete Guide to Washington Quarters.
F12. Were it a 4 Reales, I believe that is the grade it would fetch. That's one of things that's kind of nice about grading world coins, for the most part there aren't any slide shows displaying increments of wear that are supposed to categorically assign a grade based on wear of specific features. Agree the rims are too worn for a FINE, but the overall look of the coin, especially the eagle's wings and Liberty's eye give it the look and feel of a F12.