vis1974
My children went to KCS (Kings College School) and did very well. I would very much endorse your short-list; both schools are good. We also looked at St John's School but just warmed-up more to what KCS had to offer.
Both our boys were very happy, and ended up at the next schools of their choice, so all in all, a result. You only get one chance to get you kid's education right!
Good luck.
MB