I don't think our school band or orchestra plays above grade 6 - it may be partly that publishers (at least the American ones that I have seen) of band and orchestra arrangements don't sell stuff above grade 6. On the other hand, some publishers use grades 1,2,3,4,5,P rather than grades 1,2,3,4,5,6. I do know what you are referring to though as I have seen solos and competition/certification music rated higher.