Just being devil's advocate here, as I really don't agree the PAC 12 is light years ahead, more like they are pretty close to the top (which I know we agree there), but:
Alabama struggled with West Virginia
LSU was getting beat by Wisconsin (A big ten team) who was running a non QB at the position
Vandy got blown out by Temple
Ole Miss was in a dog fight with Boise St.
To answer the original question: I do think OU is one of the tougher games along with Alabama and Georgia. Florida could be up there too, if their offense actually has a pulse this year. OU is good, their ability to win out and be in the playoffs is only limited to Stoops' choke factor late in the year.