Andrew is probably too modest to suggest it but why not ask him about his Concerto for Solo Piano ?
Far too modest for that
Not as difficult as most of the suggestions:Not sure there's such a thing as obscure Chopin, but maybe the Fantasy Op. 49 is comparatively uncommon?For Liszt, the Ballade No. 2 is less difficult than most of his virtuoso stuff (and less difficult than the suggestions above). The Polonaise No. 1 is very rare and a great piece, and the 2nd Polonaise is quite tough and less uncommon, but also clocks in at about 8' only. Both are definitely virtuoso works: