Another necropost on this thread lol...
Yi-Chung Huang has some insane recordings of some of the most difficult pieces out there...
Liszt - S. 140 no. 4b (one of the hardest piano Etudes ever written)
Alkan - Op. 17 Le Preux (the octave section at the end is just absurd)
Liszt- S. 253 Spanish Fantasy (possibly the single most difficult individual piano piece, pre-Sorabji)