Hi,
An example DGX-305. Taken from one of my sequences:
voice - notes used
Jazz rhytm - 1 note
Brass section - 3 notes
Sweet tenor sax - 3 notes
Drums - 3 notes
Nylon guitar - 3 notes
Live grand piano - 3 notes
Rain - 1 note
Jazz organ 1 - 3 notes
Vibraphone - 2 notes

If I played 3 notes on vibraphone there would be a polyphony drop. Obviously, some of the voices use 2 poly. I suspect:

All live, sweet and cool voices - 2 poly
All organ sounds - 2 poly
Vibraphone - 2 poly
Jazz rhytm (yes, it is an acoustic bass and cymballs combo) - 2 poly

The real poly drops to 16. So what? It's a 450 euros low-end keyboard.

On the other hand, YPG625 delivers the same 16 true poly too, shares 99% of the DGX-305 sounds and costs 800 euros. The only obvious difference to DGX-305 is the 88 GHS keys instead of 76 lighweight. It is an expensive low-end keyboard.

I did not take into account the styles because every one style is downloadable from internet. BTW are there as many downloadable styles for Casio as for Yamaha? Do the beginner users need all the features that casios has?

George