okay i just re-read everything, thierry13 - sorry for that "outburst", had a bad day and took it out here. you're right, so here are my (hopefully) more specific questions!
1. Prokofiev Toccata op11: how to acquire accuracy and strength/"power" in the left hand jumps - my chords always seem very light and no matter how much energy i channel into the chords, it sounds weak and the more energy i try to put into it, the more wrong notes i hit.

also, what fingering do you use at bars 77-78 in the right hand; does slow HS practise work for this piece - i'm doing slow HS but do not think i'm improving very much, the notes are...wild.
2. Chopin Etude op25 no12: i've basically got the notes, this one doesnt seem too difficult, but i seem to get tired and a bit tense after the fourth page or so. how do i avoid tension? can anyone teach/tell me how to relax/practise economical use of muscles so i dont get tired easily?
3. Chopin Etude op.10 no7: this one is actually harder for me than 25/12. i dont know if the movement should come from the fingers, wrist, forearms, or shoulders. the whole etude is very easy to sight-read or merely "play" but whenever i speed up the tempo a little bit, i make mistakes everywhere in the RH. i THINK i'm playing from my fingers and arms but i dont know if that's correct.
*phew!* lengthy!