It looks like the arpeggiator feature offered in the 670 does not go up to the 770 or 970. interesting.
also, can't tell if those realtime control knobs on the 670 will be part of the interface on the upper models. seems curious if not.
Tom, the picture on page 7 of the July 2015 issue of MUSIC INC magazine shows the PSR-S970. If you look at the right side of the keyboard under Voice Effect, you will see the Harmony/Arpeggio button. This should prove to be an interesting feature! Here's the link: http://www.musicincmag.com/digital_editions/2015/1507/single_page_view/7.html