I can only speak for my area and not the schools you mentioned.
My child will not be in preschool til 4. She will be in a program that is half days, M-F. It is play based. The whole school is small and her class is small. The teachers are knowledgeable. There is very little turnover. I was impressed with the 4 yr old teacher, her continuing education, her philosophies, etc. Moreover, DD was so comfortable at the open house that we could have left her there. I was looking for something small, close by and would teach through play. I read reviews from other parents. I looked at the other kids, and watched how everybody interacted.
I think DD needs to learn to follow someone else's instructions more than she needs to be drilled on her ABCs. I think she WILL learn but I wasn't looking for an intensive academic program.
She has been home with me the last couple of years and would have JUST been 3 last fall. We decided she didn't need it. She does library time, Sunday School, and has regular playdates. She has social time. She already knows colors, seasons, numbers, counts, some simple math, letters....but I think she's ready for school and will enjoy it. ENJOYING learning is important, too. I want her to enjoy learning for years to come. If your son is already leaps ahead in academics, find someplace that will promote that, but also allow him to grow in other ways by being with different people, being in a class, etc.
I don't think my SS even went to preschool. SD went at 4. SS got an academic scholarship and SD is on her way to college. I think your son will be fine.