Hi Patekova, Thank you for this interesting comparison !
IMO, key points of the two references are:
5231J: improved technique on the enamel dial because of the 10+ years of experience on the 5131 series, and 2) font for the city ring is more usual
5131J: 1) more vibrant colors (important to me on an enamel dial), 2) no blockage on Baffin Island by the logo on the enamel dial which is already a very small surface, and 3) the crown protector gives the watch a different look
Hence for me, the 5131J has a slight edge over the 5231J.