In terms of academics, the kids who were P-12 at my school (as to 7-12) didn't do any better statistically, as far as I could see.

Ditto for sports, and music.

There also wasn't a noticeable number of people who stuck with particular friends from P-12 either ... friendships came and went and grew and morphed ...

I like the idea of P-6 at public school. It's better grounding, IMHO. I met people in year 7 who had a really, really different concept of money, travel, "normal" etc. Our realities were so very very different.