I've heard the theory of putting 2 of the Big 4 in each division of the Big Ten, so I did a little research to see if there really is the Big 4 as they've been mentioned (M, OSU, PSU, NEB).
First, if you were to use recent years as the measure of who is in the Big 4, and if you used overall winning % as the way to determine who was 'better', you would have to go back 15 years to reach a point when those four teams have the highest winning %(through present) of the 12 teams. Likely, they would continue to be the Big 4 if you kept going back in time, but that does not necessarily make for a balanced league in the present.
Likewise, the Big 4 often fall on hard times. In the past 11 seasons, there has been at least one team of the big 4 with 5 or more losses. Only two of those had only 5 losses (and winning records). The remaining years had at least one of the Big 4 at .500 or below.
In other words, keeping track of the Big 4 is probably not an important factor in deciding how to align the divisions. Also, because teams vary from year to year, I continue to propose using recent results (5 years, say) and re-aligning periodically (every year would be cool). I will go into more detail in a later post.