I am going to buy a new depth finder for the front of the boat on Monday and have decided to either go with the Humminbird 597 HD DI or the 788 HD DI the price on these two is about $650 for the 597 and $800 for the 788 and I was wondering what are the differences betwen the two. I can see that the 788 has the contour XD map on it and the other does not but that is all i can tell. Is the contour XD map comparable to a navionics or other additional map? My purpose for this depth finder is so i can see offshore humps and ledges and stay on them while standing up front and also being able to mark waypoints. Thanks for any help!