I was in a similar position last month after I sold off my Humminbird 597ci di. After many hours in various forums/bassproshops looking at the HDS Gen2/Touch/Elite7, I eventually went back to Humminbird with the 798ci SI.
Here is some insight into my thought process.
HDS Gen2/Touch - requires mounting separate gps/transducer/structure scan - Even for my PA12 this is unnecessarily complex. The second transducer for structure scan was a deal breaker for me, unless it's the newer and much more expensive Touch series.
Elite7 hdi- finally sonar plus down imaging, but the trade off is the 800x480 resolution and 256 colors. Why leverage their broadband sounder if you're not getting the full colors. Also, the single micro sd slot was a deal breaker for me. Saving your waypoints/recording on the Navionics chip is sketchy. The 7" screen would have been nice though.
798ci SI - Side Imaging is worth it! How many times have you wondered if there was something to your side worth checking out? The way I have it setup, I can see between 85-100' to either side. Though the screen is smaller at 5", it's also 640x640 resolution. Add in 3 dedicated view buttons, 2 SD card slots and the ability to record your entire days activity and then review the data on your PC. Plus it's a single transducer setup. Oh throw in a rebate and killer holiday online pricing and I got it for pretty much what retail is on the Elite7.
The major tradeoff to be fair, no 800hz for SI/DI. Nothing is perfect...
Hope that helps...