I want to raise a side question here...when one thinks of the most 'difficult' piece in the world, people tend to want to think of works by rachmaninoff, Alkan, Liszt, etc. However, composers like Messaien, Boulez (already mentioned), Sorabji, or perhaps even Schoenberg, Berg, and Weber can easily beat out any of the aforementioned composers in the difficulty of their piano works. Not necessarily because it 'sounds' difficult to play--but the stamina, mental focus, and musical understanding required to competently perform their pieces is immense. My question is, should we separate these groups of composers when considering difficulty within the corpus of piano literature?
Nathan