I've been listening to the Chopin Etudes by Cziffra a lot lately, and I've begun to think, which etude set is harder, Op 10 or Op 25 (excluding TNE here sadly, even though I love them)?
Here's my list of "points" so to speak for each set:
Op 10 has the following that are all very difficult;
10/1
10/2
10/4
10/10
Op 25:
25/3 (though not as bad as some others)
25/6 (!!!!)
25/8
25/9
25/10
25/11(!!)
Some people say Op 10 is harder purely because of the first two etudes, but honestly I think Op 25 is bigger as a whole. Unless some of the ones I specified are easier than they sound, which is possible (though usually not the case with the etudes).