I think Roland RD 64 is good, but unfortunately it only has 64 keys and no on-board loudspeakers.
Roland RD 300 is not too heavy, but again no loudspeakers.
(Yamaha NP 31 is nearly non-weighted, I guess you know that.)

What another polophony?

???

Dam texting on phone
How is the polo phony on these units.. dropouts etc.

I recently got a Yamaha CP4. I had a RD 700 NX and later a CP5, but I like the CP4 best. It is relatively light weight, incredible samples from 3 Yamaha grand pianos, good extra voices, easy to use and add a layer or split, and a real wood keyboard that feels terrific if you want to feel like you are playing on a real grand piano. And it costs less than the CP5 did- Yamaha did a nice job with this and it will be a keeper for me for a long time.

Hope that helps

The Roland models all have 128 voices polyphony, so I can't imagine you'll have any dropouts.
I forgot the Roland FP-50, it obviously has got speakers:
http://www.roland.com/products/en/FP-50/
But like the RD300NX, it's quite heavy (around 17 kilograms).

Layered sounds, two hands and frequent use of the sustain pedal can eat up 128 voices in no time. Some handle dropouts better than others, but if you're playing 2 handed piano with sustain, I'd suggest as much polyphony as possible.

The Casio Privia I played yesterday had 256 no drop at all layers etc,...nice unit.

Donny
You beat me to it, you tried the Casio. I think the PX350 is your best bet. Great keyboard feel and sounds, plenty of polyphony, on board speakers and a basic arranger unit for that sketchpad work at home. 1/4" stereo outs and ins.
I never use the onboard speakers but if I brought the piano into the house from my studio they would be useful.

the Casio px 5s the best in the under 1,000.00 it has a 25 second decay it is very good light weight and feel very good you cant go wrong with that one.