I just purchased a 998 to put on the bow and moved my 798 up front. I've only been using this setup for about a week and I have to say I really like the SI up front. You are not going always get the picture perfect views, but you can definitely see things that you would have missed otherwise. Having the SI up front allows you to select the appropriate "view" to get the information most valuable to you at any particular time.

What most don't think about is no matter what LCR sonar technolgy you use, it is displayed on a flat screen that scrolls the recorded images from one part of the screen to the other. While you get a whole screen of recorded data, ONLY the very first row of screen pixels is current data, the rest is HISTORY. If a return is not constantly being repeated on that first row of pixels, it is not within the coverage of the sonar pulse.
While fishing you want to know what is where NOW, so history is useless. That is were Side Imaging is great for bow/trolling motor use, that NOW can be returns a good distance from the boat, not just what is under the transducer.
I use Side Imaging at both ends of the boat, but about 100 times more at the bow because that is where I am most of the time. I basically sight fish all year no matter what the depth and water color is since I find the fish and fish for them directly.
A blurred screen due to turning the motor has no effect on finding structure and fish since I am only looking for current data. I can spend the time to keep the motor pointed in a single direction to get a whole screen of sharp images, BUT that doesn't help me catch fish. Some of my sharpest whole screen images have been with the bow setup that I have saved when moving along in a straight line, but that was due to changing locations with the trolling motor to fish another location.

This is a screen shot with one of my SI units on the trolling motor with a trolling motor mounted trasducer. I was just crossing from one side of a cove to another. It is a creek channel with vehicle tracks made during lake contruction.



This is another bow image taken while weaving through trees/stumps and finding a school of bass with a school of shad. I caught about a dozen of the bass just being stationary and keeping up with the bass school as they moved by turning the trolling motor--not a sharp image, but a functional image:

I constantly change the screen speed on my 997 depending on how fast I'm moving, especially with the latest upgrades. You can definitely use it with a trolling motor... even when jig fishing. If moving at .5mph (and less), I still get a great picture. I just turn the unit around, and reduce the chart speed to 1 for this.

I have a 998 si on my trolling motor. I like it but tm noise will interfere. other than that I am able to use it and maneuver the boat where I want it.