Some great 5th and 6th-ranked teams:
2018 Ohio State
2017 Wisconsin
2015 Iowa
2015 Ohio St
Wow, this has really affected the B1G, hasn't it?
2014 Baylor & TCU
2012 Oregon
2010 Ohio St
2009 Florida
Hell, in 2008, you have 11-1 USC, Penn St, 12-0 Utah, 11-1 Texas Tech ranked outside the top 4 who could win it all, easily.