Piano Forum

Op. 10 No. 5 is my best etude out of the entire set, so I'm speaking from my personal experiences.

1. Measure 45: Go for the 5th finger. It's always best to avoid the fourth finger if possible in these fast etudes that require a sparkling touch, because the fourth is the weakest finger by itself. Not the fifth, the fourth. Since it lacks its own tendon, it's very much dependent on the third finger. It's incredibly difficult to produce a smooth, clear sound in that specific passage. Make sure to put a little emphasis on the top note with the fourth finger, the Db.
It does feel less reliable at first, but it will help when you get to the correct speed. 4th finger will drag you down, most of the time.
Going down is the same story.

2. mm 65: Rubato is your friend. Don't rush it. Make the top Eb light and sparkling, then play the passage. I use the soft pedal for the passage, makes it more warm. My fingering is to play the top Eb with any finger, and play 4321 321 4321.  It's the fingering that works for me, not the 54321 or its variants. 54321 rarely works in the performance speed, as there's too much pivoting going on.

3. The octaves, when played right, can be the star of the etude. I think the key is your wrists. It should feel like you're clapping. Clap for a few seconds, and examine how your wrists move. Replicate the same motion, except on the keyboard and on the notes. It's  very awkward at the beginning if you're not used to it, but it's necessary for speed and clarity.

Just something else: Your left hand has a lot of melody as well, in the thumb. Don't neglect it, for example from measure 65 onwards. (Gb---Ab-F-Gb---Ab-F-Gb) etc.

Practice the right hand routinely, staccato, legato, dotted rhythms etc.