My opinion: if it hurts, it is not good. Piano playing or practice should not hurt. Try using the wrist to rotate (up and) around. Re: op. 10 no. 9 - true, Chopin did indicate 5-4-1 in the first edition. Your "pivotal wrist" discoveries will help.
It's exactly like sports ; you will get tired, your muscles will strain, but the more you do it, the further you'll be able to push it. You don't have to fear the pain, just keep track of you limit ; I often have pains in my fingers or arms when learning a new and hard piece, but I've never been incapacitated (and I practice a lot). For me it usually is painful when away from the piano (when writing for instance, or using the computer), and it gets better after I warm up.
I can't imagine why! You mentioned Schumann.
Well, if I remember correctly, he injured his hand trying to stretch it ; the same way Scriabin injured his right hand overpracticing (over- is the key part !). Every time I see I'm mindless repeating some painful movement at a fast tempo, I think "Schumann !" and it makes me take a break ;D
Why would you ever need a clean 11th?!
Sounds cool ? It's like octave glissandos ! you don't need it, but for a reason you want to have it.
All in all, more than a 10th sure isn't that useful, but when playing Liszt and sometimes Scriabin (though I guess it was meant to be arpeggiated then) I sometimes wish I had a better reach.
Plus my fingers aren't really cute, makes me sad. Some people I know at the Conservatoire have long and slender fingers, huge span, you know, those hands that make you gap and think "he must be a pianist !" (though I guess it's totally unrelated). I'm so jealous.
Try Scriabin op. 42#1
I'll have a look at it, from what I understand though the Op. 42 is quite hard, not only technically, but also musically.
This days, I really have huge trouble getting my Scriabin to sound the way I want ; for instance my 8-12 is note perfect at a proper tempo, but when listening to my recordings of it, I can't help but hate it. I seem to miss something, some kind of "special effect", some rubato or pedal or stacato or anything, because it sounds dull and uninteresting. Let me give you an example : for 8-12, I find the second page impossible to play nicely without using outrageous amounts of rubato ; the written rhythm is quite mechanical yet you have to make it sing (most recordings I've heard hardly follow the rhythm on the sheet I think). Does that mean I am supposed to play it "freely" ? This problem most likely includes the pedal for me : what are the choice you can make when playing Scriabin ? It seems to require more than "what's usually permitted", as in "if you don't go the Horrowitz-way it won't work".
I play the 8-2, I love it (I like Pogorelich's too) ; learnt it for the polyrythm along with the Chopin nouvelles études, and it's a beautiful piece you can play quietly or with anger, at various speed. Not everybody likes it though.
I use the pedal quite mechanically there as far as I know (like I would in say, Chopin).
Sounds like I'm venting, sorry...
I don't understand why composers leave out the pedal ; as you said, it might be understood at the time (for Chopin it is fairly straightforward, I think), but when you get to XXth century music, it no longer makes any sense to me. I've been looking for books on the subject, but have yet to find anything. Surely, the pedal has its root in the construction of the piece, like the dynamics ; when pieces get stranger like they do in the XXth, the dynamics get harder to predict (in my opinion ; the phrasing also gets different), but they are still indicated. The pedal gets harder to use, but you're still free to do whatever. Is bad pedal something you can work on in itself (a series of effect you use to emphasize parts of the piece), or is it something you only get through proper analysis of the piece (a coherent and essential part of the piece) ? I still wonder, and the "listen and make it sound good" method is very hard for me (brains first kind of playing I guess). I need reasons behind my choices...