I think 8-2 vs P5 might get us ranked higher than 10-0 against a WAC schedule. But the truth is that (over the last decade), BYU football wins 71.4% against G5 and only 39.5% against P5/ND.

So (overly simplified statistical work here, but good rough estimate) that means if we play 10 G5 teams, there's a 17% chance we win 9 or 10, which gets us ranked.

But only 16% of the time would we win 6+ against a matchup of 10 P5s (based on historical data). 8+ wins happens only 1% of the time.

So it's not a decision between
undefeated against G5 OR
8-2 vs P5

It's a decision between, once every 6 or 7 years,
Going undefeated or one loss against G5 (like this season) OR
Going 6-4, maybe 7-3 against P5 competition