Chris Mullin (ahem) started HS at Power Menoral for their BB prowess, let's just say, he was more athlete than student (nothing wrong with that), but being from Bklyn, he and the BB coach at Xaverian had a connection so he went there when Power closed its doors.
Xaverian at least back in the 70's was considered the premier Catholic HS in Bklyn (after Jesuit Bklyn Prep closed) and most of the Boroughs. I don't know if its academics have kept up over the years. Back than it was up there.
Agree with your assessment of Regis totally. Beleive me, the really really smart kids in my large Catholic grammar school went to 1. Regis (we had 5 there), 2. Xavier (5) and 3. Xaverian (a 5-8), the rest went to mostly less expensive Diocesan high schools supported by our local parishes. In the very beginning these high schools charged little to no tuition.