Mike,
If you are running the latest software in your 798ci Si unit you should have the ability to sort waypoints by the following: “A to Z”, “Z to A”, “Newest”, “Oldest”, “Distance”, “Icon”. To do so, open the “Waypoints, Routes, Tracks” menu and select the “Sort By” selection near the top left of the menu window.
For HumminbirdPC: while viewing your Waypoints; move the cursor over one of the column headers (“Name”, “Icon”, “Shared”, “Visible”, “Latitude”, “Longitude”, “Depth” or “Date”) and select it. Doing so will order the waypoints alphabetically/numerically from the lowest value. Selecting it a second time will list them in reverse order.
For what you are trying to do you may want to try the “Distance” selection on your Humminbird unit and the “Latitude” or “Longitude” selection in HumminbirdPC.