Really the key differences are down to hardware/WiFi, if you go here and go down to the routers and click compare you can add them all to a table to see the differences:
https://www.netgear.com/gaming/Other than that a few software differences - XR300 doesn't have Smart Connect (the automatic smart switching between 2.4/5GHz WiFi based on device need).
XR700 has extra features such as Plex but no specific DumaOS differences.
