I've got the Casio Px350. It came out before the PX5S. I agree the action is first rate and the piano sounds are great. It differs from the PX5S in many ways but as a basic piano it is the same but with built in speakers. It also has a very basic arranger section which would be OK for a cocktail hour or similar backround music gig.
I think the PX5S is more aimed at being a Pro Midi contoller/Master keyboard and the 350 more of a all around home keyboard.
For the price either one is well worth it.
_________________________
Bill in SC --- Roland BK9 (2) Roland BK7M, Roland PK5 Pedals, Roland FP90, Roland CM30 (2), JBL Eon Ones (2) JBL 610 Monitor, Behringer Sub, EV mics, Apple iPad (2) Behringer DJ mixer