Using AP for this exercise

2013: 163-23 (.876)
2012: 171-23 (.872)
2011: 158-26 (.858)
2010: 165-17 (.906)
2009: 163-22 (.881)
2008: 162-22 (.880)
2007: 155-30 (.837)
2006: 161-23 (.875)
2005: 146-22 (.869)

This is the relevant top 15 for playoff selection. The final top 15 has the winning percentage depressed due to the top teams playing each other in bowls. Winning percentage is .874 (1444-208), which still puts us below average historically.

I agree with you that the goal shouldn't be to schedule three-four expected top-15 and go undefeated. That's a suicidal recipe and one that teams finishing top 4 (regular season) hardly ever do. However, in order to make the top 4 for playoff selection, it's not implausible that we'd need an undefeated season with 1-2 victories over (final regular season poll) top 15 teams, and once there we'd need to defeat two additional top 15 (top four) teams.