Regarding how good can one get -- the term used by the research is expert. But, at least in the papers I read, they don't make it clear what expert is. For example read:
http://www.ida.liu.se/~nilda/Anders_Ericsson/Ericsson_delib_...
But in my own personal theory... you become Michael Jordan by doing the 10,000 hours+ and having innate gifts. You get a basketball scholarship (D1-D3) by doing the 10,000 hours.