Hi, I've just started year 13 as well, and basically in the same boat as you. When I saw this thread I was pretty glad I'm not the only one struggling with this decision.
Basically from what I've read and heard (threads on here, meeting with admissions tutors, speaking to students (my sister is at Cambridge)), your grades are perfect for oxbridge. You're perfectly capable of making a competitive application, as long as you have a passion and love for your subject. I think I remember reading on here that the average number of A*s for successful Oxford applicants was about 9? So you're set.
Furthermore, the only way to emphasise your abilities would be through your application and interview. I'm not sure because you're studying medicine, but have you sat the BMAT yet? If I'm correct, both universities require it and so that would give you a chance to really show them just how good you are. Also, if you got an interview, that's another chance to really show off your skills. At the moment, I have no idea what Cambridge are doing with UMS/raw marks (I've asked on the admissions tutor thread so hopefully I will get a response), but I know for sure that Oxford does not take them into account.
Well done on your amazing results!