As a professional pianist speaking, that Pa4x sounds to me like one of the best sounding keyboards for pianists (or one of the best sounding "demo's?). I also thought the Rachmaninoff bit in Donny's P700 posting had excellent sounding pianos and the strings behind it....dynamic!
But there's more than the sound...it's got to feel right in your hands. That's a toughie, because once you play acoustic, electronic NEVER feels right. I have that kind of a problem when I switch from piano to accordion.