What does it matter how Bear Bryant performed when we are talking about Bo Pelini and who might replace him. It doesn't. I'd rather see how his peers perform in the same environment.
The same environment would include things like the same amount of tv revenue, same amount of donor and booster support, same quality of facilities, same level of fan support, same strength of schedule, same advantages and disadvantages of recruiting and same quality of players.
Which is why comparing Bo to all currently active head coaches is the least effective and conclusive thing you can possibly do if you actually want to measure him properly.