I got those figures from a previous post in this forum (it's still there but several years ago..). I'm surprised SHS told you a percentage - problem is that there isn't a 'pass mark' as such. SHS (and all the other Glos. Grammars) pass the top however many (this year SHS seem to have passed about 250 I think - not come across anyone with a ranking lower than that.) scorers in the exam. Therefore it follows that on a year where the papers are hard or the cohort more average, a lower percentage will be required to gain a pass mark.
I tried my hardest to work out what my DD would need to score - highest score you can get on each paper is 141 (although this doesn't necessarily equate to 100%...) and I think the lowest is 70, but someone else might be able to put me right. 70 doesn't mean a getting none right though - it's all got something to do with statistics which is beyond me
Anyway, my DD scored 241 which gave her a rank of 122. I know because I've got her scores from Ribston and Denmark Road that she did better in the second paper (106 first paper, 123 second paper for Ribston, I think). Judging from what my DD said about the exam I think she probably got between 75% and 80% right on the first paper and max. 85% right on the second paper. She certainly made a lot of mistakes on the first paper and rarely hit 90% on harder papers so I doubt very much she got an average of 85% over both papers.
Girls who scored a fair bit lower got places this year - DD's friend scored 223 and got in.
If I were you I would aim at 90% in most papers, but not worry if your DD doesn't get that high - average of mid 80's is probably fine. Time management is crucial - moving on from difficult questions promptly to get to the end of the paper, and then going back for another go if there is any time left.
I will stop rabbiting now..time to go to bed!
Hope I haven't confused you even more.
I'm not at my most coherent this time of night!