I applied to Cambridge this year and got an offer for HSPS , and from my experience they look at a lot of things , not just GCSEs (pretty sure Oxford put more weight on them). Generally my GCSE results were good , 9s, 8s , 7s but I had a 4 in further maths and they managed to overlook that. Basically , I think it's still definitely worth applying as there's so many other parts of an application (predicted grades , entrance exams , essay submissions, interviews , personal statements ) all of which are more important to Cambridge. 7s are really good (still would be As in old grades!) and Cambridge looks at all data contextually, so as a fellow bad high school alumnus haha , I would definitely encourage you to apply if it's something you really want to do. Sorry if that was really rambly but please don't think you need all 9s or anything to apply!