I'll give it a shot, but I've never had a case so far where it doesn't try to upgrade on first boot. In the straight "out of box" experience it forces the upgrade.
It probably won't be catastrophic, but it would make me nervous since we've been testing the app only on 6.0.1 up to this point. I can upgrade one of the tablets here to 7.1.1 and run some tests, and assuming the app generally runs okay, then worst case we can probably live with a 7.1.1 upgrade if it happens. Still, we'd feel far more comfortable knowing that the version of Android the judges are testing on is the one we tested against.