Kirt, I have the quadrabeam on the transom of my Nitro, I run the Humminbird 777 on that ducer. When I bought a new trolling motor for this same boat a couple years ago I bought an 80# Maxxim without the US2 and put a quadrabeam ducer on the trolling motor but the cable was so thick it was messed up within 30 minutes. If I remember correctly it runs at 520Hz, it is not side imagining by any means but I still like it. One other thing it is not the Plus model that you are referring to and I don’t know the difference between the two. I would imagine they did some sort of enhancement to an already good item.
A couple other thoughts I forgot to mention, you referred to the side scan was twice the depth on my unit the side scan is the same as the depth. Quadrabeam has less data to process making it faster than side imaging. I don’t know for sure but I think I can read to the sides at 35 mph.