Colley matrix poll the most and don't care much about AP poll. BYU is #6 right now in colley poll which is based purely off how many wins and how many wins your already-played opponents have. BYU would get a short term boost in this Colley poll if KSU beats OSU.
under the tiny chance that BYU would be in contention for an at-large playoff bid at the end of the season, it won't matter what the opponents rankings were at the time of the game but rather will be the opponents' rankings at the end of the season. And since we play both, then that is a wash.