If the tremolos give you trouble, try practicing them somewhat more slowly and with absolute evenness. Actually, if you do them accurately and evenly, speed is not quite as important.
Even Liszt wrote much more difficult music...Sonata in B, most of the Transcendentals, Totentanz, etc.
Actually, I've always felt that Sorabji's most difficult piece was the Cyclia Sequentia Super Des Irae (or something like that, anyway) It's fully as difficult as the O.C., and twice as long. Needless to say, it's never been performed, although one of these days I'll buy the score just to look through and play around with, lol.