Here are some thoughts based on raising three gifted kids (one with an LD as well) in one of the worst ranked states in the U.S.
1. Figure out why you want or think you should put your kids in preschool. If it is because you work and want your kids to have something better than daycare, then look for something that will give your children opportunities to explore new experiences or an academic track. It will be nigh unto impossible to find a daycare that is going to challenge your child academically, so pick experiences such as field trips to museums, lots of hands-on activities, etc and a positive, nurturing environment. If it is because everyone and their dog goes to preschool, consider bypassing it. None of my kids went to preschool and all did perfectly fine starting Kindergarten. It was nice to have a few more years with them since I stayed home.
2. You will find sucky teachers in the best of schools and amazing teachers in the worst of schools. That being said, finding a school where the majority of parents have college degrees will likely mean you have a better support base for the school and more pressure on the administrators to meet the needs of the higher IQ kids. But where you live should be about the lifestyle and environment you want for your kids, not just the school district. We choose to live in a high poverty state with not so hot schools because we love the culture, the weather, the opportunities to do things outdoors and nearby access to family.
3. IQ - the baseline IQ you'll find at age 3 may be very different than when your child is older. Unless you need it to gain entrance into a specific educational institution, I'm not sure I'd subject my child to the arduous testing when they'll likely have to do it again in a few years anyway. You know your kiddo is bright; you know they're going to learn faster and deeper just about whatever subject interests them, so I'd probably spend more time exposing them to new experiences so that their world of ideas is expanded rather than worrying about a specific number on an IQ chart. On the other hand, if you see significant gaps in abilities within your child, then it would be prudent to test to determine if there is a developmental disorder that could benefit from early intervention. My youngest is twice exceptional, and I wish I had listened to the doubts I had when he was younger. I often wonder if he'd still be struggling so hard with his dysgraphia and dyslexia in mid school if we'd tested earlier.
