For anyone stressing about the SPGS exams yesterday, I am a current SPGS parent. It is very common for girls not to finish papers and so I would really not read anything into it if your's didn't - mine didn't finish the paper that they said she had been particularly strong in!
Also, anecdotally (but from a former SPGS teacher who had been involved in the exam process), a rough litmus test for how they are expected to perform on the maths paper would be c.90% on section A (the basic arithmetic section), c.75% on section B (the standard 11+ style section) and c.40% on section C (the "puzzle" style questions). As I say, that is anecdotal but it correlates with how mine thought she had done.
I'm slightly loathe to comment on numbers getting through to interview as I understand application numbers have been going up and they may be inviting larger numbers to each stage after the initial computer test. The general rule of thumb was that around 20% or so weren't invited to sit the exam (based on around 500 applicants and 400 being invited through to the exams day). Then roughly 200 would be invited to interview and around 115 places then being offered, together with a relatively short waitlist (of which some will be eventually offered places).
Good luck to everyone going through the 11+ process - there is light at the end of the tunnel!