Sometimes I start extremely general topics just to see what kind of responses I'll get.
No harm in that, as far as it goes...
For example, in the "Anything but Piano" part of the forum I've started two topics "Jesus" and "Is there a God?"—it's quite awesome to see people argue over a few lines of text.
Well, it is surely not too unreasonable to suppose that those two topics might be of serious interest to some readers...
God speed.
Should we assume from this that you do believe in God - and that He operates at a high metronome mark?...
verbose and obfuscated writing à la Hinton;.
Have another look at my initial response to your opening salvo; whilst it's true that it did not answer your question as simply as you might like (i.e. with the title of a single Sorabji piece), preferring instead to challenge the validity of your question, if that response is either verbose or obfuscated, then so's "Mary had a little lamb".
sorry I couldn't fit in more grave and acute accents,
Why? Where? (or is that too many difficult words?)
But enough of this. Let's at least try to approach the question seriously. What kinds of difficulty might we be considering here? There are several, including but not limited to
1. Musical / interpretative difficulty
2. Digital dexterity
3. Mental agility and concentration
4. Mental / physical co-ordination
5. Mental and physical stamina (particularly in the long works)
6. Projection to audiences in public recitals
most of which may be thought to pertain in extremis in some of Sorabji's most demanding music.
But then should we not also be thinking about who it is that encounters the difficulty? It is likely that the questioner has in mind pianists (which is perfectly understandable), but what about listeners, or conductors of the orchestral works (most of which have yet to be performed, admittedly), for example? And what about organists? - an interesting case, due consideration of which must take on board the fact that only one organist in living memory has ever tackled Sorabji's organ music, whereas in the past 30 years or so, a far greater number of pianists have performed his piano music.
Obviously, Sorabji's large-scale works are likely to be thought of as those containing the greatest degrees of difficulty of all kinds. Of course, OC is always mentioned in such a context (has any visitor to Piano Street not encoutered it somewhere? - I seriously doubt it!) - yet there are quite a few other works of 2 hours or more in duration - including all three organ symphonies - many of which have yet to be performed. Even if we concentrate solely on those large works for the purpose of finding the answer, it would be well-nigh impossible to do this with any degree of reliability, since it would be a daunting task indeed to assess unperformed works in terms of any kinds of difficulty and then compare them to performed works, would it not?
Over to anyone else with other ideas...
Best,
Alistair