Based on your repertoire, I would suggest a Rachmaninoff prelude. Op. 2 no. 1 or 3 would probably be a good fit (a bit challenging based on the pieces you've studied) but still doable. If you want to do something a bit more challenging, look at op. 23 no. 5 or op. 32 no 12.
If you still find those pieces lacking in virtuosity, try
-Liszt's Waldesrauchen, La Leggerezza, or Un Sospiro
-Chopin's op. 25 no. 10 - would probably be a perfect duration, but based on your repertoire, it doesn't seem like you'd be comfortable with the octaves.
-Rachmaninoff Moment Musical No. 4
-Liszt's 10th Transcendental Etude
-Rachmaninoff's transcription of Mendelssohn's Scherzo from a Midsummer Night's Dream
Something not romantic that hasn't been mentioned - Prokofiev's Toccata. You'll probably find this very difficult past the first 2 pages or so.