Hi Udo
I have a PSR-S910 and Tyros4. To me the size of the keys feel the same, but there is a different feel to it when playing. Difficult to describe, but I would say it feels a bit lighter.
I played a S970 in the music store and to me it feels the same as the S910.
I think the S970 is a great keyboard, but the Tyros5 is just superior and in another class.
Regards
Rudi