I know teams like to overdraft QB's because of the position but in recent years QB's with questions in their game have dropped. I think Petty, although he's being hyped as the third best QB, will fall. Look who fell last year:
Manziel, almost fell out of the first rd, but he fell quite a few spots
Bridgewater, to an extent fell quite dramatically considering he was the consensus #1 QB
Mettenberger, fell from round 4-5 to round 6
AJ McCarron, fell from round 2 to round 5
Derek Carr, again not a huge fall, a lot had him going in the 1st but ended up in the 2nd.