The YPG-535 has the bare minimum polyphony available for a digital piano
at 32. More complex songs, regardless of the skill of the player, are nearly impossible to play accurately due to sustained notes being cut off once the limit is reached. Simple and staccato songs will sound just fine, but for smooth, flowing tracks one will have to look elsewhere. More at http://bestrateddigitalpiano.com
With a polyphony of 128, the DGX650B is aptly equipped to play virtually any song. 128 is the general magic number when it comes to maximum polyphony: few players will find themselves ever needing more. Regarding sound however, the keyboard handles its maximum capacity better through external speakers than it does its own. More at http://bestrateddigitalpiano.com/what-is-the-best-portable-digital-piano-that-you-can-get-today/
Casio PX850 Privia
The PX850 features a maximum polyphony of 256, which is very nearly absurd. Like the higher gears of most supercars, few players will ever find themselves playing fast enough and sustaining enough notes to ever hit the PX850’s
capacity. However, some will come to appreciate being able to play more than 128 notes at once, if not the full 256. This keyboard simply gives players enough room that they’ll never have to think about filling it all.