I carry a total of 10" on JoJo
But, unfortunately 2 x 5" sets.
One is a combo and the other just chart, so in effect a backup plotter, as both have maps.
Mine are Lowrance units, chosen because I won the combo unit! But I don't like to talk about that, much!
I had put Lowrance on my previous boat and this boat came with Garmin I think, which was ok but I missed the Lowrance.
Eagle used to be the same as Lowrance, though am not sure if they are still available.
I would have thought 7" would be best for a unit you want to see from the deck, or fit an on deck unit like Nigel has for drifting wrecks ect.
Rob