Sweetpeas - I would try to ask the schools if they:

1) have experience with profoundly gifted children or those who are working at x grade level in reading, writing, math or whatever subjects; schools may question what you're saying, but it's still worthwhile to ask.
2) can accommodate such children and how.
3) are children in mixed-aged group setting - your child may not want to stand out like a sore thumb in a setting with her chronological peers who are not functioning at her level
4) is the curriculum flexible and fairly unstructured/structured - this can make a big difference
5) I would ask what happens when a child exceeds a grade within a matter of months and whether they are bumped up a grade or provided with the next grade level material or not.

Of course, some schools may try to fib, but you might be able to get a better idea on whether a school is willing or able to accommodate you or not.

I don't know if you've seen this link on pg kids or not, but I found this useful - http://www.davidsongifted.org/db/Articles_id_10115.aspx

I found that most gifted schools are still based on a traditional classroom (subject-based, teacher-driven, one-size fits all curriculum where everyone is working at a similar pace) and not aimed at pg kids. More often gifted schools can accommodate when a child is advanced in reading, writing, or math but not when it's all three or more subjects.