If I went for the GTN650 then I would go for the 750 also, because (like the 430) once you are used to an MFD, even my old KMD550, the 650 screen is too small to be used as the primary display for the route etc.
I think in most aircraft one would go for analog links to everything, including the EHSI if fitted, but would use ARINC to drive an autopilot if possible (to get decent roll steering).