I have been through the early kindergarten issue, so I'll let you know my experience. My older duaghter's B-day is 10/5. As you said, the state's cut-off is turning 5 by 9/1 to start kindergarten. I wanted her to be in Madison School District, and they will actually test any kids with B-days between 9/1 and 10/1 for kindergarten, so we missed their cut-off by only 4 days. My daughter had been reading since 3 1/2 years old, and was very academically ready, but many people cautioned me about her emotional readiness, and worried that she might fall into more of a follower role because of her youth. I was also at home with her fulltime and she had never been to pre-school at all, but she has never been shy.
Anyhow, we decided that she really needed to start school at 4 years old. I just worried that if I kept her out until she was nearly 6, that she might be bored in kindergarten. I found Montessori Day School Public Charter (at 14th St & Dunlap), and they were willing to test my daughter, and found her to be ready for kindergarten. She did very well in kindergarten, and even though she is a little younger, she remained assertive and a leader. I didn't initially tell her that she was starting earlier or that she would be younger than most of her class, though. Though she has now figured out that she is a little younger than most of her classmates, I didn't want her to go into kindergarten worrying that she was littler or anything. I didn't put her in preschool before starting full-day kindergarten, and she did great. She loved starting school and being there all day was fine with her. She's never been especially shy or clingy, though. I cried like a baby when I left her school the first day, while she just smiled and waved! After kindergarten, we moved her to Madison Simis for first grade, and she is also doing very well there.
I honestly believe that we made the right decision in starting her early. After over 2 years of being a reader, her reading has progressed to the point that she has been put in the advanced reading class for 1st grade. After doing kindergarten last year, she is also advanced in her math, and is in the advanced math class for 1st graders. So, I think that if she were in kindergarten just this year, she would probably be too far ahead and maybe bored. With her very assertive personality, I'm actually glad that she is on the younger side of her school peers, because she can get bossy, and if she were on the extreme older side of her classmates I would worry about her running them over. She is actually a little tall for her age, so she isn't any smaller than her classmates. In fact she is about average height in her class. As I said before, she has recently come to notice that she just turned 6 in October, but all of the school friend's birthday parties that we are going to are for kids that are turning 7. I've just told her that she'll be turning 7 later this year (2009), too.
We don't have any allergy issues, so I can't really advise you there. I can tell that at Montessori Day School the kids all bring their lunches and eat in their classrooms. They might be able to make some sort of provisions if a student has severe peanut allergies. My friend's son has a severe peanut allergy and his preschool classroom was appointed as a peanut-free zone, but that was at another school.