Was wondering whether top level 5 and KS3 topics are required only for Sutton schools or is this the case across all grammar schools in different areas?
The only reason this standard is required for Sutton is because Sutton grammars welcome applicants from a vast area and because thousands apply for relatively few spaces. It isn't the schools themselves that dictate the standard. To gain a place requires achieving a higher score than many hundreds of bright and well prepared children therefore the successful candidates are even brighter or even better prepared.
In more fully selective areas, where there are lots of grammar schools, the standard to gain admission may not be so high simply because the schools prioritise local people (so reduce direct competition for places) and have enough room to take many more who pass the test. In some areas the top 20 or 25% of all pupils can go to grammar school whereas in Sutton that is far from the case.
Equally though, there are other regions just like Sutton which are hugely competitive and where the entry standard therefore goes up and up.