Thanks all for answers. One final question. I see that most casio models from that time at least uses the same AIR sound processing. Does that mean the piano sounds are almost identical in quality from px 160 to all the way up the price range including px5s? I know that px5s has way too many ways to synthesize unique sounds but the sound quality on a regular piano patch would be the same as the lower models or not?
Only if that is the case, and since even a px 150 would have the same sound and action, if I only wanted to play with the piano sound and didnt care for additional features, would getting px5s be worth it? I like the capabilities of px5s but if I will get the same sound and action with a px 150, I might let go of extra features of px5s and go for px 150. Yet if you say that px5s can have a noticably better sound, I would go for that one instead.