i think the most difficult Chopin etudes (10/2, 25/6, 25/11, etc.) would be more difficult than all of the Moszkowski etudes. but just flipping through, Moszkowski's 72/13 seems as difficult.
i think a part of Chopin's etudes' difficulty lies in the "unreachable" tempi, e.g. 25/11.
By contrast, (on my copy) the Moszkowski has no specific speed request.