"You can't plan on the basis of what might or might not happen. You can only plan on the basis of what is happening."
However, you don't know what IS happening, becuase your source of information is an Ofsted report which talks about what WAS happening, over a period of 1 or 2 days, up to 3 years ago. Equally, data on 11+ entry from the school is historic.
To find out what is happening now, and much more importantly what is likely to happen in the future (because your child isn't even old enough for school yet, let alone getting to the point of 11+ etc), you need to visit the school and to talk to them. It is extremely likely that if an issue with the progress of able children was identified by Ofsted, there is a huge amount happening round able children in the school at the moment. To find out, you have to visit, and talk to them.
FWIW, before my (very able, on the ASD spectrum) DS started school, I was probably a bit like you - worried about how they would cater for his ability, keen to 'get him reading' [shouldn't have bothered, he taught himself before I ever thought of getting round to it], wondering about the quality of the school and where it fed into etc etc.
Then DS started school.... and the things I had worried about / you are currently worrying about weren't a problem at all. It was the social / emotional / practical side of schooling, that I hadn't really focused on, which tripped us up ... so much so that I would say that the ideal preparation for school is nothing to do with reading or counting, and everything to do with being able to eat a wide variety of foods, completely independently, in a busy dining room; being absolutely independent and as reliable as possible with respect to all aspects of toileting; skilled in all aspects of dressing, undressing and getting changed; being able to form friendships and work co-operatively with both individuals and groups of children, whether those children be 'like you' or 'completely unlike you'; and being able to take instructions from all adults and then carry on an activity independently...