Is band 6 for sciences only 80?The syllabus says "simple" number proofs so I think the other content will be the source of the harder questions.
Considering some of q15 in 2015 went to q16 in the sample paper, it looks like it might have already been a bit easier than 2015 even before any editing (79 ish band 6?). If they did make the exams easier it might become similar to sciences (low 80s?) or if they just kept the nice aligning anyways it might stay as mid high 70s.