looking at the specs, there doesn't appear to be much difference...but, sonically, there is...of course, this is my personal opinion having played both instruments extensively.
Same for the difference between the Motif XS and XF, on paper, apart from the Flash Ram, not much appeared to different.
But sound wise, there is a world of difference.
This is what I am now starting to anticipate will be the same with the PA3. Styles, for example, will have the same name, but sound radically different....
Time will tell for sure.