I have had some of those issues with DD3. I am working on just being comfortable with who she is and if others have a problem with it, letting it be their problem. When she was not-yet-3, she started reading refrigerator magnets in front of a house guest, and I made the mistake of saying, "Oh, she's not really reading; she just has a bunch of sight words." But DD heard me and told me for the next several weeks that she couldn't read (despite the fact that she had literally hundreds of sight words and could read many first-grade readers without help). It took some work to undo that mistake. (But she is over it and I definitely can't make that same claim now, as she reads just about anything these days.)
For me, part of feeling more comfortable is going to the library and acting like it is no big deal when she picks a book at random and starts reading (instead of hurrying her out like I used to do). Part of it is having a forum like this one to share what she's into. And part of it is just getting over myself and realizing that all kids are different and it really doesn't much matter where she is compared with other kids. I think if you are relaxed about it it shows and others won't be as uptight about it. Oh, and if you are in a playgroup where people are constantly comparing milestones, find a new one.
AFA preschool is concerned, I wouldn't do a sit-down-and-learn-these-specific-things kind of preschool. If she is interested in something, definitely explore it with her...but try not to make it formal or push her. She may have the abilities of a 5 or 6 year old, but she's NOT 5 or 6. And she needs free-form play much more than structured education, IMHO. It's not as if she won't be picking up amazing things anyway.
