I play all the Brahms op. 116, and I play the Chopin Etudes you mentioned. They are very difficult pieces for different reasons. The Chopin Etudes are for obvious reasons. Upon first impression, the Brahms did not appear so difficult - "just" a lot of sound and passion - but get into it and (especially in nos. 1 and 7) you are presented with so many problems! The rhythmic hemiola, the big legato sound, articulation (yeah, see those rests and staccato notes?), pedalling...took me a while to put them all together, and even now it's still somehow not quite right!