I hate to say, but I don't have a big romantic piece, but I know one that is 3 to 4 minutes long. Humoresque Op. 101, No. 7 in G-Flat Major by Antonín Dvořák.
One of my all time favorite solo pieces is actually the alkan "overture" I believe it's op.39 no.11 Crazy difficult, I've only attempted small parts of it
My vote goes for the Barcarolle! Very challenging piece for pianists both musically and technically, and such an indispensable part of the romantic repertoire.... A great project to learn all kinds of things about voicing, rubato, musical inflection, and beauty!
I agree, I think it is one of Chopin's most beautiful works. Be careful though, it will challenge your athletic abilities at the piano in ways you may not yet realize! The jumps in the final section, when the theme comes back ffEven just the very first page contains a myriad of technical and musical difficulties which take a master pianist to navigate with any real elegance. I would say it is harder than any of the four Ballades. Have you played many of Chopin's Etudes?
Rachmaninoff Coreli Variations.Your search is now over!!!Go ahead and start learning it!