Even with my years and years of piano lessons under my belt, I have abnormal difficulty with large leaps and transitions between large chords, but fast single-note runs (e.g. scale runs) are fine and tremolos are OK. I can also keep up fast repeated-note runs without switching fingering for short periods (generally by vibrating my hand). I am not good with cross-rhythms: I already struggle with 4 against 3, and the only one I am confident with is 3 against 2. I can deal with regular syncopation and mixed meters better, though. Likely adding to my struggles with some advanced pieces is the fact that the largest interval both my hands can play accurately is an octave each--I always play adjacent inner notes if I try to reach a major or minor ninth.
For example, I find Rachmaninoff's famous Prelude in G Minor, Op. 23, No. 5 to be more difficult than claimed.
This is one example of how a comprehensive difficulty rating can prove hard to implement.
