If it's going to be your main fish finder, I'd go with the 798. I bought one this spring for the front of my boat and love it, although I don't use the SI much up front. Also, if this is going to be your main unit, I'd get the navionics option as well.

I have a HB 1197 at the Console and I use it's SI all the time. The thing is, when I'm on the trolling motor, I'm usually not going fast enough to get an optimum picture from the 798's SI. ( 3 to 6 mph recommended)