Source?
Also, this depends on the cohort doing the exam, the exam difficulty, study design, and exam format. So it's unlikely that it will be the same. Exams at the start of the study design (e.g. 2017) are often easier than exams at the end of study designs (e.g. 2016). However, there's also a new exam format.
Really, it's hard to tell and you shouldn't be worrying about how many marks you can drop because that'll just make you stress more.
They're based off my alterations of others over on the SS estimator forum, who said that losing 10 marks will get a 45, and losing 20 marks will get around 40. This year's exams have 120 questions instead of 140, so I made the necessary alterations. I'd say that this year's exam was difficult, but so was last years (the 10 marker from last year is the great equaliser), therefore I'm hoping that the cutoff for A+ and 45 are around the same. These are just my interpretations, they shouldn't hold any weigh and you shouldn't really based off what I'm saying to make any assumptions (DISCLAIMER).
I also hope that due to the level of difficulty being on par (hopefully) with last year's exam, Psych will scale up 1 instead of scaling down 1 (if you have a study score over 40). I've been lied to by the ATARNOTES calculator for the whole year, as it said that psych still scaled down (based off 2016 results).