What is he passionate about? Let him learn about what interests him at home - surround him with books and experiences that will feed what he is passionate about right now.
Both of my DC were reading very well at 3. They "took off" when surrounded by what they loved: books, experiences, and letting them "research" topics of interest.
I haven't worried about testing until there has been a specific need for it. DD was not given any tests until her school did them. For DS, he wanted to attend a special interest class this summer that happened to be for "gifted" that had a test score requirement. He took the WJ-III Ach. at 4.5 y.o. so he could attend classes at this center. He did extremely well, but I do wonder that even at 4.5 y.o., his scores might be inflated because of his age. I think that threads on this board have discussed potential unreliability of testing at a young age, but if you are very curious, you could turn to testing.
I also completely agree with Mana about the advantages of having an early reader. My DC have taught themselves various things because they could read - it is a beautiful thing. I also agree that working at home, while adding in a "socialization component" (part-time preschool, classes, sports, etc.) gives a nice balance.
