Let's look at the 4 undefeated teams Out-Of-Conference Schedules.
Oregon: New Mexico, Tennessee & Portland State.
Auburn: Arkansas St, Clemson, La-Monroe, & Chattanooga
TCU: Oregon St, Tenn Tech, Baylor & SMU.
Boise: Virginia Tech, Wyoming, Oregon St & Toledo.
Looks like TCU & Boise have played the tougher OOC schedule.
I think OOC strength of Schedule should be a BCS factor.
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Why only OOC strength of schedule? Auburn by far plays a tougher overall schedule than Boise or TCU, even with it being relativity easy by SEC standards (all hard games at home with the exception of Bama and Miss State, and state).
Boise and TCU play one, MAYBE two tough games all year, whereas the Barn, and Oregon play several.
For instance, Auburn has played:
Miss State (much improved, and a solid top 25 team)
South Carolina (SEC east champ, and one of two teams to beat the defending national champs)
Arkansas (they can play with anyone at this point)
LSU (more than likely a BCS at large team)
Georgia (a down year, but the talent is still there)
Alabama (defending national champs, two losses. One to the SEC East champ, and one to a probable BCS Bowl team)
If Boise or TCU had that schedule week in and week out, we wouldnt be having the conversation that they should play for the Nat Champ.