For any help it can provide:
Physics - depends on the difficulty of the exam, but in 2009 it essentially required full marks in both. Perhaps one lost mark would have been acceptable.
Chemistry - much more leeway for lost marks. However the 2009 Chemistry Midyear was considered pretty difficult by the cohort. Still, one would think losing 4-5 marks over both may be acceptable
Methods - unless there's a tough exam, one can probably only lose 1, maybe 2, marks in methods over both exams.
Specialist - last year the exams were considered fairly straightforward, with the tech active very calculator heavy. In that year 1-2 marks over both was enough to get a raw 50. For a scaled 50 one could likely have lost 5-6 marks over both. In a year with harder exams you could probably lose a bit more than that.
So you can judge your capability for yourself. But if you work hard and set your mind to it, then the courses generally aren't that heavy on content and the focus is perfection of technique and prevention of silly errors. If you can do that then 50 should be possible
