Here are the pro/cons that I see
Part-time Preschool - Skip K
Most preKs are focused more on social skills with some academic skills mixed in. It would give him time to develop socially, and he could be home with you a good part of the day so you could work on some of the skills he'd need for 1st grade. However, there is a big jump in expectations from preK to 1st. 1st grade requires long periods of sitting in a desk from day 1, and the writing demands are pretty high out of the gates as well.
Early K
Kids enter K with a wide range of social and academic abilities, so he might not be as outside of the box as you think. A K teacher would more likely be able to meet his academic needs than a preK teacher, and it would be an easier transition into the non-academic demands of 1st grade.
However, my thoughts are based on the average experience. You might get great teachers who really get your DS, or you might not. IME the school philosophy is important, but the individual teacher is more important.
