This is nothing but a hunch, but I tend to have good ones.
I would guess that musicianship talent would be correlated somewhat with hitting early milestones in general, and also with innate calculation abilities. I would expect musicianship talent to be linked to higher-level math skills to the rough extent that innate calculation abilities are linked to higher-level math skills. I would expect musicianship talent to be linked more often with higher-level musical abilities (composition), but that of course is explainable in large part through interest in the subject.
