@FE2022, the website has some general information on leavers' destinations and scholarships, but not a breakdown of numbers by destination. It hasn't been updated for a couple of years but is still reasonably representative.
https://www.spcslondon.com/about/destinations-of-leavers
SPCS isn't really a feeder to particular senior schools so tends to send small numbers to a wide range of schools at 11+, aiming for best fit for each individual child. It's quite a small cohort compared to some prep schools - around 32 pupils in Year 6 and about half will leave at 11+ (most of the girls and a few boys). A large proportion of families live in North London so tend to go for senior schools that are easily commutable from Camden/Islington/Highbury/Stoke Newington/Hackney.
For co-ed, Forest is a popular destination, with smaller numbers to Highgate and the Northbridge House schools. For girls-only, CLSG, Channing, Queen's College, the Francis Hollands, and sometimes Blackheath or JAGS for those living south of the river. SPGS isn't really on the radar, but I think that's just geography; academically able girls tend to go to CLSG. For boys-only, CLSB, UCS, sometimes Dulwich. Wetherby Senior is becoming a more popular destination for boys. Boys aiming for Westminster (1 or 2 per year) stay until 13+. Academic and music scholarships at 11+ (and 13+) are reasonably common.
Some parents cast the 11+ net wider, e.g. with the intention of moving out of central London - for example, within the last few years I've heard of 11+ places offered at NLCS, Habs Boys, Whitgift, Eltham.