Etude No. 50 is similar to No. 48, but focuses primarily on diatonic (instead of chromatic) scales and arpeggios. Suggested tempo is quarter-note=104-120, although a more brisk Presto can work as well, provided that everything is clean without sounding frantic. The “espressivo” marking is interesting, and there are probably several ways to interpret it, including shaping the phrases through dynamic changes (beyond what is marked), varying the intensity and strength of articulations, and perhaps even a small amount of rubato.