If you can handle five, do it, but to be safe just excel in four!
And I have to say R.S. isn't art based- it's classified as a humanities, and contrary to popular belief it's not considered 'soft'!
&& for medicine, in RS you touch on medical ethics and obviously other ethical theories in general which could work in your favour as a talking point in your p. statement...IF you were looking to do a 5th subject, you can't go wrong with it.