GPS & Depth Finder Combo Unit

We've pulled the trigger on a center console Gator-Tail and we're trying to figure out which unit to get. Mainly looking a Humminbird and Lowrance. We'll use the boat for duck hunting and fishing the marsh as well as some lakes in central and south LA so we want good gps functionality, but also want one that is useful for finding fish/depth/structure. Most of the units we're looking at have the 5" screen, but I don't know if that's big enough for my FIL to see and read accurately. Would like to get suggestions/advice from those that have experience with the combo units. Thanks in advance.

One of the units recommended to us is the Humminbird 688...seems like it would do the job, but I'm not sure about the size of the screen.