Joachim Raff's '3 Klavier-Soli' Op. 74 are virtuosic etudes designed to develop specific pianistic techniques. They often feature brilliant passagework and demand considerable technical command.
The primary challenge lies in mastering rapid arpeggiated figures and maintaining clarity at speed.
3 Klavier-Soli (Op.74) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 8.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
3 Klavier-Soli (Op.74) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.