I have a November baby and we agonized (x a billion!) over what to do about sending her to school. In the end, even though she was bright i.e. knew all her abc's 123s, colours etc.. she just wasn't ready. When I would bring up kindergarten, she'd say "kindergarten, why would I want to go to kindergarten?" (She was in preschool at the time, in the school where she would be going to kindergarten).
One of my friends was doing her doctorate in ed.psych and she also had a november baby, exactly one year before I did. She consulted her professors. They unilaterally advised her, if she had any doubts, wait. It is far better for your kid to be ahead of the curve than constantly struggling to catch up. Also, guidance counselors i consulted said that it is very, very obvious in junior high who the youngest in the class are. They may be smart, but socially, a majority struggle and a lot of times, those differences in maturity don't come out until junior high.
So we decided on a second year of preschool and waited to put her in kindergarten. It was the best decision we ever made, at the end of that second year of preschool she was all about "kindergarten, kindergarten, yay kindergarten!!!" And also we had the added complication (unbeknownst to us at that time) of the fact that we ended up moving all over hell's half acre and she ended up fitting with her age-peers in every school system we entered - all with different entry deadlines. she was always one of the older ones in the class but she's extremely quiet and introverted so she could use all the extra confidence she could get.
She has always LOVED LOVED LOVED school. Always. and it continues now that she is in University. Keeping her back a year was the BEST decision we ever made.
I know how hard this decision is. Good Luck! I know that you will make a very informed decision that will be the best for your little guy, no matter what you decide!