The main prediction that comes to mind is that if Christianity is true, one would expect substantially more miracle claims by Christians (legitimate claims plus false ones) than by any other religion (false claims only).

This also assumes there isn't some saturation point of people only wanting to talk about so many miracles. (Ignoring buybuydandavis' point, which probably interacts with this one in unfortunate ways.) If people only forward X annoying chain emails per month, you'd expect X from each religion. The best we can hope for is the true religion having on average slightly more plausible claims since some of their miracles are true.