Just to add, here's another rating provided by a guy named Alan Chan (from his website https://www.geocities.com/alanchan1048576/mus/music.html)<very easy> 7, 20, 4, 6, 2, 15, 21, 11, 9, 17, 13, 10, 23, 3, 14, 1, 18, 5, 12, 19, 22, 24, 8, 16 <very hard>I think though that the one Bernhard gave above is more accurate. I see only one error - #17 and #11 must be interchanged; undoubtedly, the latter is much easier (and much longer) than the former. In #17, there are lots of cases in which fingers tops over each other; also, there are many shifting in chords. #11 is just as easy as #3 and #1.(BTW, what does ABRSM mean?)
K I'm not a 'piano master', and I find number 5 very difficult to get used to, so I skipped it and went to others I could play... I don't feel I have to play them in order.... I'm not going to be ready to play number 16 before number 20....
Consider yourself a real virtuoso if you can play num 8,16,19 and 24.
I can play the aformentioned preludes (8, 16, 19, 24) without much fuss.The easiest of the 4 for me is the 16th one, and I usually play it at a metronome tempo of around 220, sometimes reaching 280 at the middle part.The hardest is the 24th- one wrong calculation in turning your fingers on those up and down scales can lead to disaster, but the part where there is a downward chromatic thirds scale is not much of a problem.