One good reason to have the PX5s having less notes say 64 is it would be the lightest SHORTEST weighted keyboard on the planet but 73 would be better. Its the best and most likeable/playable keyboard I have ever had, and I've had about 20. I have waterfall keys on my hammond kx3c and they don't compair to the Px5c when I midi it. The keyboard on the PX 5s after having had a roland, kurzweil ,yamaha, rhodes, (and lots more) is just the best and WORKS for me. What is the principal thing about the px5 I would say the piano What must a piano have? Weighted keys