I am thinking of perhaps learning Fantasie Impromptu soon. I have played a 4:3 polyrhythm before but not for longer than a measure. The piece in which I have encountered this polyrhythm is Nocturne Op. 9 no. 2. I am perfecting that nocturne(I commonly lose my place in the rallentando when I start at tempo and go up to trill speed).
I noticed that my hands, even though my right hand is the same width and depth and is only longer by a millimeter or 2(that slight asymmetry in the hands I found is due to handedness, my longer hand is my dominant hand), my right hand is more flexible(don't get me wrong, my left hand is pretty flexible too). This shows up clearly when I play arpeggios that have a 10th as the interval between the lowest and highest notes.
Take the first 2 arpeggios in Fantasie Impromptu for example. They stretch up to a 10th. I can't reach a 10th with static intervals at all in my left hand and I can rarely reach a 10th in my right hand as a static interval.
I can use a 1-2-4-5 fingering in my right hand for G#-D#-G#-B but for that same arpeggio in the left hand I have to use a 5-3-2-1 fingering(Both of these are with some rotation to reach the 10th without overstretching the ligaments). Only when the interval is a 9th or smaller can I use a 5-4-2-1 fingering in my left hand.
I don't know if I am going to get a growth spurt in my 20s or not(I know some people do get a growth spurt in their 20s). But I was wondering, would practicing Fantasie Impromptu, particularly those triplet arpeggios, increase my left hand flexibility, particularly between my 5th and 4th fingers?