Sonar advice needed

[Johnp]

Preparing to outfit a soon to be purchased Revolution. I have been looking at Lowrance units. Main goal is fish arches but hdi bottom structure would be nice.
Looking at the Elite 4 HDI combo and the HDS 5 Gen 2 with nautic insight. I may actually be able to get the 5 for less than the 4.
Now for the variables: The 83/200 will fit the hobie well, the 50/200 probably not and the 50/200 combo for the elite four definitely not. West Marine tells me the 50 /200 is needed for good arches.
My thought at this point is go with the 5 forget HDI ( which might not be that great past 100' ) and mount inside the hull if necessary. I think I have seen a lot of 5,s in use, and I think a guy told me he was able to modify it to fit the Hobie inset.
Any advice is greatly appreciated. Thanks.