To Send Or Not To Send.... That Is the Question

We have been debating on whether or not to send the boys to school next year. They are in their second year of preschool right now and according to their teachers they are very respectful, social and are good listeners. However, when it comes to letters, numbers and writing they aren't behind for their age but they are for the class. I didn't realize how young they would be for their kindergarten class if we sent them next year. They will just be turning 5 in June so they could be at least a year or more younger than some of their classmates.
This issue has become a big source of stress for us. I have went to a kindergarten readiness speaker, talked to other moms that have kids that started early and kids that started late. I have also spoke with their teachers and other kindergarten teachers. All in an attempt to make a good and informed decision. I don't want one kid to be behind and at the same time I don't want them to be bored. I want them to socially fit in and not be the kids in high school that are growing a mustache as a freshman (although with their genetics I don't think this is a concern). The feedback I have gotten has been that parents never regret sending them late but some have regretted sending them early. The feedback from the kindergarten readiness speaker was that a kindergarten teacher has the amazing talent to take kids from different ages, races, backgrounds and academic readiness and get them all to the same point by the end of the year. Wow! Kindergarten teachers need to be paid more. That sounds like a very difficult job. The feedback from their preschool teacher was that they were socially ready but could probably use another year to become more confident in their ability to do academic activities. We put a lot of weight on her opinion since she has been teaching them for 2 years now. The other input I got was to "red shirt" them (which to you sports fans probably makes sense) in other words keep them out a year so that when they play sports they are bigger, older, more coordinated and stronger than the other kids. Now take a moment to think about the freshman from your high school with a mustache, that's what his parents did, he was "red shirted". Although I would keep my kids out of school another year so that they are emotionally and academically ready I would never keep them out for the sole purpose of them being better in sports someday. I don't have high hopes that our genes somehow made a great athlete either. If you know us you know that another year will not solve the coordination problem.
So, our final decision is to wait another year before sending them to kindergarten. They have the next 12-18 years to attend school. They may as well be kids for one more year while they attend the nature based preschool that they have come to love.