As a long-time preschool and kindergarten teacher, and also the parent of kids who were very early readers, I have a few recommendations.
First--do have him tested. That will give both you and the schools you're considering a firm idea of exactly where he stands. The schools will be able to tell you how he'll fit into their curriculum and how they pan to address his needs. That will give you more concrete information on which to base your decision. (Having the testing done is also quite helpful in another way--it helps the schools see that your concerns are real, and that you're not just a pushy parent who thinks her kid is more brilliant than anyone else's kid.)
Secondly- a little brainiac who is less mature than his peers may not have a good social experience in school. If the school can give him enough academic stimulation so that he doesn't act up out of boredom--and any good preschool should be able to do that--there's no reason to push him ahead.
Finally-and perhaps more importantly--I wouldn't underestimate the value of kindergarten for your child, regardless of his academic skills. After several years in which the trend in education was more formal teaching at younger and younger ages, we're now beginning to see that kids were suffering from a decreasing amount of time in which to just play. Unstructured free time--time to think, daydream, follow their own interests, and maybe even do nothing--and in your child's case, read--has a great impact on nurturing children's creativity and their enjoyment of learning. He'll spend the rest of his childhood sitting at a desk, so an extra year of a good quality preschool could be a great gift.
BTW there's an article in the July 28 issue of the New Yorker magazine called "The Eureka Hunt" that discusses the brain science of how people, like inventors, get insights--and unfocused, unstructured time is definitely a factor.