I think it's important not to get too hung up on the leaf grade. Grade 1 is definitely not necessarily 'better' than grades 2-8, in fact some people would shun bings made purely from tips in favour of bings made from larger leaves. The grade just refers to the size of the leaves and how they get sorted by a machine (such as the one here). My personal preference is for bings with larger leaves as I feel there is more depth of flavour and huigan to be extracted from these leaves than from pure bud bings.
Also it is my understanding that a recipe will not necessarily only contain 1 grade of leaves eg. an 8582 will contain grades 8,7,6 leaves but the majority of leaves will be of grade 8. It's my understanding that it is these proportions, along with blending of different areas which make up a recipe.