Sorry for not getting back to you earlier. rnvinc is pretty much dead on for comparing detail.
I ran my 798 for almost a month on my console before taking delivery of my other rig with the 1197 and it's deafinetely worth it. I have the internal GPS with my 798. You can run split screen in SI/2D and be able to read them, you just have to get pretty close to the screen if something appears on the SI screen, unless of course it's detailed and large. I run crankbiats alot and was able to sit right in fornt of unit so screen size was not that big of issue.
The 1197 is far more detailed for structures than my 798, but it's mainly due to the screen size at least from what I can tell. I run it in slit screen quite often on the river as I mainly look for the ends of the wing dams and L dikes as well as anything laying behind them. I been using SI more than the down imaging mode as well. If you run a 998 on console and a 798 on bow, I am pretty sure you will be happy. I was going to get a 998 but only went with the 1197 since I was able to get it with the new rig.
If you can find a dealer or someone that has the 798 already mounted in a boat at the console, this is the best way to get a real feel for how it will suit your needs. I never liked the way these shops Cabelas/Bass Pro put these units on a shelf all crammed together and expect someone to get a feel for operating them in the boat. Cabelas started mounting a few of the different units in boats so anglers could get a better idea.
I would rather buy a unit that I was able to see a demo while standing in a bow of a boat than having someone smacking away at all the neat little buttons reaching up on display shelf.
If you were closer I would be more than happy to take you out for a real demo.