My dd now5 was similar - she learned to read and talk at the same time - and learned to speak many words from reading them. The only "negative" I saw was that for a long time she would pronounce words while speaking as though she was reading them - so she would always say "bean" for "been" - and still calls sewing "Sue- ing" - she is otherwise fine though. Both of my kids did go through a period of pretty severe stuttering - and that went away on its own - I think it has something to do with having so many new words in their heads, but not yet having a ton of practice retrieving them.
