i sense that a post by mr. hinton is coming....
his most difficult pieces, so i hear, are his sonata V "opus archimagicum", sequentia cyclica super "dies irae" ex missa pro defunctis, and his symphonic variations. apparently opus clavicembalisticum is too easy to be considered in the top 3. their grades would be somewhere around 100, i would guess. but why worry about his hardest pieces, unless its out of curiosity? id try to find out what his most doable pieces are. in my mind, the pastiches and maybe the nocturne-ish pieces are most doable. ive never tried playingany sorabji, which explains why im still alive.