FWIW, I personally don't think that attainment of "best in field" as you call it is necessarilly automatically qualifies someone as a genius. It's certainly a term that is used very frequently these days.
The kind of focus, single-mindedness and work-ethic displayed by those such as you mention is certainly a form of savantism and in all likelihood, could also be attributed to a form of aspergers or even autism. For extreme cases of this you need look no further than the likes of Derek Paravicini and Steven Wiltshire. These, together with those you already mention are undoubtedly incredible examples of how talent manifests in so many different ways, but genius?
It seems to me that the "label" genius was historically used to describe those that were truly exceptional across many, many areas of expertise. The old renaissance types if you like. I guess the world has changed so massively that those types are never likely to be encountered again. Interestingly (at least to me anyway) many of the renaissance types were (and still are) criticised for their "inability" to finish things but (as I understand it) this was down to their passion and desire to do and change as much as possible. This is almost the opposite of how most might typically characterise a savant. Still very tortured mind, but quite different in my mind from the torture and anxieties that a savant probably faces.
On that same topic, I don't believe Derek Paravicini is tortured by his own mind, far from it in fact, although interestingly there is the possibility that Steven Wiltshire might be, but only as a result of treatment designed to improve his "condition" which appears to be having the effect of reducing his savantism.
It's a massively interesting area though isn't it? Personally, given half a chance I'd sign up for Allan Snyder's transcranial magnetic stimulation research (if he ever subjects it to wider study) as I too would really like to understand so much more.
