20 MB can be enough for a quite good piano. The Yamaha factory pianos in the Motif XF don't have more! I just downloaded the CP1 piano package for the Motif XF, it is better than the on-board pianos. I checked how much data the main waveform group takes (including 5 dynamic layers plus key-off sample): it is about 60 MB. Nowhere near The Kronos with its 2 GB piano, but nevertheless sounding excellent!