Your last point is big.Tend to agree, but:
1. I think $25M would get it done
2. If they add teams (SDSt, SMU) who bear the burden of unequal sharing for the initial GoR period, that could be a source for UW/UO to get more (say the 2 newbies get half share, and UW/UO get 1.5 shares). I think the M4 could tolerate that.
The biggest thing against the PAC is the Prisoners Dilemma. First one to cut a deal is safe, so there is intense pressure to not be the 2nd Prisoner and get left behind.
The exposure and $ are going to get a lot of attention. But the most critical element for the Corner 4 is going to be a GOR by Oregon & Washington that spans the length of the upcoming Big10 deal. If Oregon & Washington have an out to join the Big10, then the Corner 4 lose their leverage with the Big12 if OR/WA jump ship. And the Big12 could require the Corner 4 take a partial share to join the Big12.