I have a 798 that I hot swap between my triton and war eagle. One unit seems to meet all my needs the way I have it currently configured for both boats It will not fit in the dash of my triton, so I set-up duplicate RAM mounts on both boats...each has its own transducer. The photos's below are the War Eagle mount.
I have used this unit for two years and have been quite happy with it...once I spent time to "dial-in" the settings. However, after using it the display is small and I have decided I now want a bigger screen. When I get a few more dollars, I am going to buy the new 998.
I think with what you describe, you will be happy with the bigger unit where you fish most. Remember the SI/DI units are not for use at speed unless you mount a second transducer in the the hull.