I think we all know the outlier seasons to test the limits of these proposals are 2008 (Big XII 3-way tie) and 2012 (3 SEC teams in top 4 before championship week).
5 Conf champs + 2 At-Large + 1 G5
2008:
Big XII Champ: #1 Oklahoma
SEC Champ: #2 Florida
Pac-10 Champ: #5 USC
G5 Rep: #6 Utah
B10 Champ: #8 Penn St
ACC Champ: #19 VA Tech
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Now first of all, screw this. A 19th-ranked team in any 8-team playoff is crap.
Secondly, even if you shrug and say they won the ACC, they earned their way in, look at this:
#3 Texas went 11-1
#4 Alabama went 11-1
#7 Texas Tech went 11-1
#9 Boise State went 12-0, and if you're a proponent for G5 teams getting in, the Broncos have the bad luck here of G5 Utah being ranked higher.
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Anyway, so we let in Texas and Alabama, right? Despite Texas Tech beating Texas and having the same record? Say what you want, but in this case, we're right back to square one of helmet-osity and rewarding early losses over later losses (UT lost earlier than TTU did).