Well, we lose the GPS signals (jamming) all the time in the mentioned ME region on the G650 - but of course we have 3 IRS to fall back on for DR. Ususally it´s not more than 20 minutes at any one time - before they start coming back up. I guess the regions you refer to will let you down on the lack of dme/dme updating. What stage(s) of the flight is your concerns at - I´d assume cruise with airway fixes?