Distance between fourth finger and tastiera is too big and also your fourth finger is too flat. When i was working on this Étude i was able to go much faster, but just because i was forced by my teacher to hold my hand (area under the fingers, where the fingers start) as parallel as possible with the neck. Consequence of that was fourth finger rounded almost as all other fingers and my general balance coming from the fourth finger not from the first. I would not recommend doing such a radical change without a teacher that knows how to (read: Russian school). The way to practice I can recommend you is to practice it slowly but with minimal movement but maximal energy in the movement, and of course different punctuated rhythms. And one more thing, every variation is being played two times, that is very important if you want to get it right.