I think you should check-out the Garmin RADAR's. The 4208 is just the display that you are driving. The 4208 is a chart plotter/display.

In the past, a 4KW unit (generally) used to be considered superior to a lower powered unit. The higher power gave you more penetration and ability to adjust the unit for fog, seaway, and wind conditions. Having a bigger array (larger diameter) on the transmitter used to make a difference in resolution -- i.e. the ability to differentiate targets. I've found that the "auto" settings work well in flat water, without rain or seaway clutter. Otherwise, you really need to adjust the various settings to get the kind of results you expect to provided by the radar unit.

https://buy.garmin.com/shop/shop.do?cID=151

I would spend the extra couple hundred dollars for the narrower bandwidth option (i.e., "HD"). I would probably go with the 24" unit BUT THAT MIGHT NOT BE worth the extra $800. I guess, if cost were an issues, I'd go with:

One VERY useful feature in an AIS and Sirius Weather options. But, then that's adding some $'s.... ;^)

I don't know if the MARPA capability requires a rate measuring fluxgate compass for this unit. As I noted below on our Furuno 3D system it does.