Well, as expected, I can report back that all three are way beyond me at the moment!

If I had to put them in the order which I would find most difficult, I would say 50 as the most difficult, followed by 46 and then 47 - dare I say that discounting the key signature, this one didn't look quite as challenging as the other two. That said, when I last played from this book, I was stuck firmly at number 31 and that hasn't changed!
I seem to remember that I was struggling with number 23 about a year or so ago (the one with the staccato octave leaps) but am pleased to say that this one was much better when I played it just now.
Clarimoo, it's a lovely book - not sure whether much of it would be too easy for you but you might like to use it for warm ups and certainly the latter pages I think are grade 8 and beyond!

I must look out for 50 Melodious Studies - have to say that I wasn't aware of its existence!