Mid 11+ for DD but did this all with DS a couple of years ago. We did 13+ and were told St Pauls got around 500 applicants, interviewed 300 for 90 places. But they only make 90 offers the unaccepted places are carried forward to Ysar 8 Sep exams for those on the waiting list to try again.
Westminster interview only around 250 so quite a few boys got St P interview who didnt get Westminster. KCS 270 applicants, interview 120, offer 60 for 30 places. All from 13 + open days a few years ago so things may have changed. I just wish the girls schools were as open, but I guess they have more moving parts and a compressed timescale.