A lot of families do end up moving closer to the selective grammar schools once their kids are in Year 9/10 and the GCSE homework kicks in. In Year 7/8 a lot of them do not mind commuting, make friends doing it, enjoy the independence.
It is quite important to figure out how you will order the schools before 31/10. There is such an incredibly short window between deadline of CAF and getting results, especially if you did a few tests across London.
My DS was not even tutored last year, we started prep last minute in the summer holidays as he was not up for it before that, he was completely focussed on his music practice. He did pass and for some extremely competitive schools, so one never ever knows what will happen. I think often people do get cold feet last minute and second guess their decisions, but I probably would be sending a DC to second stage HBS, as others have said, many are likely to get through especially on the waiting list. Unless you have another school that is guaranteed via catchment now I do not think I would let that go now. I think most of these schools do then have further visits/induction days.
My DS is in Year 7 (I do not want to say which exact superselective) and he absolutely loves it. Being around boys like him and having eg Astronomy society and visits from Oxbridge students as well as sports as well as music and a really broad and interesting curriculum, it really is fantastic for him.