As I understand it I need the G5 or GI275 for the GFC 500 anyway. Love the extra backup battery capacity also. I don't have the second air data computer for the 7" so it's just an MFD.
In a perfect world I'd add a 750XI and the second air data computer, but it was just more $ than I was willing to spend at this point. I did want the 7" as I am told it will operate in a reversionary mode as the PFD if the 10" fails. Then I still have full access to the audio panel, radios, etc. I also understood that the G5 will operate as the primary air data computer for the 7" or 10" if the one connected to the G3x fails.