I have not seen a specific list for the 997 and 1197 5.310 update, but assume it is very similar to the 5.210 update for the other units.
12/6/2010 12:00:00 AM - v5.210 This release has changes that affect the following areas: DownImaging, SI Terrain mode, SI Navigation, Custom Chart Menu, Downrigger Menus
Biggest part of this seemed to be the SI Terrain or Contour mode that removes the water column in SI view.
Robert