Should we aim for a through train or prep school

[WCC1985]

We will be moving to UK and settle in London shortly. We've got 2 boys aged 9 and 5. Have looked at a lot of info online and asked around and so know a bit (but certainly not enough) about schooling in London. Done some online tests and my best guess is that for the elder boy, his innate ability is somewhere around the top 10% of those in the same age. So based on info I got, for 11+, he wouldn't make it to grammar schools or those top independent schools. But at that level, what kind of mid range independent secondary schools can he aim for? We are flexible to as where we live.

Also, we called a number of independent schools that are through to 18 (year 13 ) or 13 (year 8), because if he got into these, we would have more breathing space and be relieved of the 11+ exam pressure, or at least for some years. But then of course, only those "easier to get in” or whose student body is very transient have spaces or have very short waiting lists.

Now, if my son got into these, particularly those through to 18, how much would they go to discourage my son to try the 11+ exam and aim for the higher ranked schools?

And in general, in my situation, would you suggest us to settle in a less academic through train school, or to go into a prep that ends at year 6 and have a tough go at the 11+ exam?

Just joined here as helping DD look for London schools which have a good arts focus as well as strong curriculum. We have been looking at Abercorn for the past few days, and have been told they will be expanding to Year 9 and beyond from September. Impressive Central London premises too. I just spotted this article from a few days ago too. I like what I'm seeing so far. educationbusinessuk.net/news/10032022/schools-must-play-vital-role-eradicating-gender-abuse-and-bias Research continues, so these forums are invaluable.

Replying late as I am new here and have been researching Abercorn for DD's children. Its a lovely school, and some research shows pleasing record for getting kids to good senior schools without some of the pressure cooker feel of some prep schools. Seems strong for the arts and they will be going to Year 11 and beyond from September, having acquired a new building. Looking in Sussex too as DD might move more permanently to her house there, Cumnor House looks wonderful from research so far.

UCS is a lovely school in NW London - no need to do 11+ once you are in the junior branch/pre prep so worth enquiring about occasional places.

For 2022/23 wanting "through schools" City of London School (boys) and City of London Girls School are both now extending into nearby prepschools.
They are offering exam free through entry to the two senior schools (both of which are ranked among the very best in the UK).
Fiercely competitive entry requirements for external candidates so this may be a gentler way in. If only I'd known this before ending up at the 11+ route.

Be sure not to confuse the new City of London Academy schools with the two private ones