@Wrinkleflint Christians historically was best, PBC overtook briefly, Christians back on top again. Very little between them, both very comfortably in top 20 in country. Probably pivots on who has the best Maths teachers to give them the edge. Certainly, if you have no attachment to either school you should be happy enough with the first of them to offer a place.
... ah, now @mishmased surely, if you're so interested in private education for your son, you would only consider the same for your daughter!!! Get her on the waitlist for Scoil Mhuire pronto. Or, sign her up for their junior school now.
In terms of progression to university, then I think the order of schools is Scoil Mhuire (girls, private), CBC (boys, private), PBC (boys, private) Mount Mercy (girls, state), St. Angela's (girls, state) possibly then Regina Mundae (girls, state). What all of these schools have in common would be a recognition by the vast majority of parents of the importance of a decent education and a commitment by them to making sure their child does their best. Scoil an Spioraid Naoimh (boys, state) and Christ the King (girls, state) would also perform very well.
For your son, Scoil an Spioraid Naoimh is a perfectly fine school. It does not have all the facilities as CBC and PBC. The average results will be significantly lower BUT the top performers are certainly capable of achieving 625 points. Opting for a grind school from 5th Year is sometimes chosen by parents. A friend has done that recently and would say that it is a son problem and not a school problem.
For your daughter, if MMC is a viable location, then I would recommend sending her to St. Catherines' National School if you can. This gives a cast-iron guarantee of getting to MMC. It's a small school so this may be as difficult as getting her into MMC eventually. However, it's located in a golden triangle between UCC, CUH, MTU, Bon Secours and the MFR Business parks. The hospitals and universities have highly paid staff who often are in situ for a specific tenure and then move back nearer their home places after gaining experience. This means that vacancies can arise in older classes. It's always worth enquiring. Next best option for primary is Scoil an Spioraid Naoimh (CailÃnÃ), then the admissions order for primary feeder schools is Scoil Mhuire, Glasheen, Gaeilscoil Uà Riada, Wilton, Scoil an tAthair Maitiú, Togher, and Ballinora National School.
Another advantage of MMC is location, often parents will want to keep their student out of the city centre and all the distractions that has. Very sporty as well as academic.