Some general thoughts in no particular order.
-- Oxford is wonderful but there are lots of great medical schools and plenty of excellent medical students at each one. It is unlike other subjects in that people rarely care where you went to medical school.
-- Your focus should really (I think) be on the long-term goal of training to be a doctor rather than the (very) short-term detail about where you study. If you are offered and reject a place this year, you might end up with nothing next year and have lost a pretty major gamble.
-- You can work/study with, at, for, or in Oxford at any other point in your future career.
If you are rejected by all four institutions this year (very possible if it's GEM) then by all means apply to Oxford again next year. If you are offered a place somewhere else then I personally would grab it with both hands.
DOI: I was rejected by Oxford, studied medicine elsewhere, and then came full circle as an Oxford postgraduate student and employee as well as being a member of Congregation and three very pretty colleges...