My child is in year 5 and we have been in the UK for less than a year. We searched for a lot of websites and it seems the academic ranking of the 2 is quite similar, St Paul's may be higher overall but in some years King's is higher. Also, their Oxbridge acceptance seems quite similar, St Paul may be only marginally better and sent a bit more to US colleges.
However, among our friends, not just foreigners like us but also locals, they seem to have a firm pecking order in mind: Westminster, St Paul, King's, and almost all in this order, with some considering the gap between Westminster and St Paul only marginal while the gap between St Paul and King's much wider and some even consider King's half a notch below. All these don't quite match the academic results (A Level and GCSE) I saw on the school websites.
Can someone provide any insights? We are still new to the country and are in the learning process. I know the topic may be a bit sensitive to some, so I am equally happy if comments are provided via private messages to me.