oh the double notes has been no problem for me. i tried my own method of getting that down that has been very effective. what i'd do is, just play the first five notes (so the first double note set is played), and just stop, then the next group of 16th notes + the doubled note. and on and on, slowly but surely, that melody is quite clear now. the problem i get is around the last and sometimes second last group of 16th notes where everything seems to blur (ever so slightly, u can still hear the notes), but i guess more slow accented practicing will help that out.
btw, i watched horowitz play this on that "Last Romantic" documentary (in a rather unorthodox tempo) but my god was it beautiful, i got so many ideas from his playing it was amazing.