mad_jock - interesting situation - although I had not thought of it - the mobile phone is an excellent idea.
I suspect the multiple screen failure is to do with ESD immunity - older devices were often crap. It has improved massively on modern stuff ( by design,statute requirements and testing), but as all this kit gets more sophisticted then it could still be possible (but they are required to recover). G1000 recovery time from re-start is about 20 seconds basic and 60 seconds AHRS.
Not sure I see the difference between two G1000's (which infact they are) and an Avidyne with a Garmin if you are suffering from such catastrophic failure? Given that the Avidyne cannot re-boot in the air I would be extemely worried about being near electrical storms.
Just because it is sold as a "system" - just remember each panel is an complete system (e.g. a 430/480/530). That is appart from power etc.etc.
ALSO I want lower power when on stby battery - so too many seperate instruments on backup power = less time to survive.