For example, some schools are claiming a 5 is a B others a C. Am I right in understanding next year a 4 won't be a pass so that will make the 5 equivalent to a C?
They aren't true equivalents.
A 4 is a standard pass
A 5 is a good pass
Speaking as a teacher, I found the easiest way to get my head around it is to stop thinking about how they match across.
Grade 4 - standard pass. It's sort of like an old C, probably achieved by the old C/D borderline students. Will get you into post16 vocational options and workplace training. Can study A levels but probably not advisable.
Grade 5 - good pass. Really where most students should be aiming as it gives you the best shot at almost a level 3 courses. Probably the benchmark for studying a level courses. Most likely what top unis will want as a minimum.
Grade 6 - Secure good grade. Excellent preparation for a level. Lots of middle set students will probably end up here.
Grade 7 - Sort of the old A. Specs are harder but this is where your higher sets are working towards.
Grade 8 - probably top set in great schools. If it helps, it's loosely an A*. It's a bloody good grade to get.
Grade 9 - the best of the best each year. Grade 9 students are exceptional, not just in their school but within a national cohort (which is why as previous posters have said it's stupid to be issuing them in school). Crucially, a child being very bright does not guarantee them a 9, nor would it be reasonable to expect that of them because it is norm referenced