The more expensive one has shaded relief. The other one doesn’t. Shaded relief doesn’t come into play until you are zoomed out a fair distance. The lake maps are identical. And the previous poster is correct that the HD doesn’t work in the elite series because they can’t do shaded relief.
Looks like an HD chip will work in an Elite 7 according to Lowrance website. I dont know if it will give you shade relief or not, but I still would buy the Pro.