We went to a psychologist for testing of our January birthday DS when he was 4, with the plan to listen to the advice of the psychologist as to whether to do early entry or not, since I was for it and DH was against it. Our DS scored in the PG range, and the psychologist told us that we may as well let him play another year, go to kindy with agemates but ask for differentiation, and then skip 1st, which in our area is basically a learn to read and do very basic math year. She said he'd likely need accommodations througout his schooling, and may as well wait a year. In hindsight, this worked out well for us. DS was very sensitive and clingy at 4, and he refused to learn how to write before he started K, he's smaller than most agemates, and he had never done FT school before. The kids do a lot more fun things in K and learn to "do school". The school did end up differentiating and DS then skipped 1st. The only issues he has had was with writing - he's still not so great at it, but it's getting better now in 3rd. We found that our skip to 2nd wasn't enough in our local school and transfered to an accelerated program for HG kids. Because your district has GT started in pre-K, maybe things will work out better for you.
Kindergarten with agemates, even with a bit of differentiation, was still tough for DS academically. He was way ahead of everyone else. Also, it was a loooong day, and DS was pretty crabby and tired for the first few months, like most kindergartners I imagine. I think it would have been worse if he had gone straight to first, though, just because it was more academic.
Just some of my thoughts and experiences. You know what will work for your kid best. It can't hurt to investigate options though (the likelihood of the school letting your kid skip first if necessary). Also, can you ask the psychologist a few more questions and let her know why you're unsure about early entrance? Maybe she'll have some good answers.
ETA: There was actually a half-day option at our kindergarten, but most kids didn't do that. We chose not to because it was just the academic subjects, which seemed kind of like torture to a kid who already knew it.
