I was just testing this for myself without having noticed this thread...I get
466-477 skill: 54/512 (10.55%)
479-485 skill: 55/512 (10.74%)
486-505 skill: 56/512 (10.94%)
507-510 skill: 57/512 (11.13%)
Faerie Piccolo adds about 16/512 (3.125%). The very strange thing is that the skill bumps happen in different places when I sing without Faerie Piccolo:
491 skill: 39/512
492 skill: 40/512
I'm not sure how to explain that. Perhaps the Faerie Piccolo effect is calculated before the conversion to x/512. That might also have something to do with how the skill bumps are also oddly spaced, they don't happen every N skill.
Interesting to see that it keeps going up into max skill range, guess I'll have to start carrying more skill.
XI Wiki

