My dad has offered to send DC to private school, though it's not something DH & I have necessarily considered. I went to a boarding prep school when I was younger, and loved it, but it was when my dad was in the RAF so it wasn't a mega-posh one.
Living close to Winchester it seems that our options are St Swithuns for DD (currently in y4 but would go there from y7) and Pilgrims/Winchester College for DS (currently in y1 and would go there from y3).
I don't have concerns about them turning out all arrogant, unable to relate to all people etc as I think that largely comes down to the parents and how they bring up their DC. I also don't worry about the academic push/ exam focus as that exists in the state alternatives anyway. My main concern is that St Swithuns and WC seem worlds apart and whether one DC would be going to a 'better' school than the other? And another question is whether it's ok not to board at WC as I'm not sure how I feel about boarding.