What I am thinking about now is that a GTX 45R would provide Backup attitude to an Aera 660.
So one option is to skip the planned backup EFIS (G5) and put that money into a 45R instead of a 35R, Then I would have ADS-B In as well and weather when flying in the US. Problem with this thinking is that the G5 with the optional battery is a great stand alone backup, if I use the 45R/660 as backup then I need to provide a more fault tolerant electrical system...
Yes, if I want ADS-B in and ADS-B weather then I need another toy
But the GDL 50 or 52 does not require any additional antenna apart from the built in one, the 52R does...