Some interesting random GCSE statistics...
For the average Oxford offer holder, 78.4% of their GCSEs are A*s. Fine Art is on the bottom (49.8%) by over 10%. Perhaps unsurprisingly, Medicine is at the top with 92.2% on average.
Now looking at A and A*. The average is 96.3%. The range is much narrower, with 87.2% for Philosophy and Theology on the bottom, going up to 100% for Physics and Philosophy (meaning all eleven people who took over five GCSEs and got into Oxford this year had all A/A*...).
As always, please remember that these are just averages, and there are lots of people who get in with significantly less top grades.