Look at 2011, 2015, and 2016.
2011 - Utah wins. BYU ranked #25 only in the coaches poll at 10-3. If 11-2, could have been top 15 in all major polls.
2015 - Utah wins. BYU unranked at 9-4. 10-3 might have achieved a ranking at least in the coaches poll.
2016 - Ditto 2015.
1988 and 1999 were two other possibilities for rankings with a win over Utah.