doing a concerto movement as a piano solo (i.e. solo and orchestral part where the solo stops)
OR
doing a concerto movement with one as a solo on 1 piano and another on another piano playing the orchestral part???
out of my editions of the Chopin 1+2, Beethoven 1-5, Grieg and Rach 2, all bar the Chopin have a 2nd piano, and the Chopin does seem excessively long to play as a solo piano.