Do you really believe that over the last 10 years that the Big 10 's post season performance is much different than the Big12's?
Your question was intriguing enough for me to look it up. Although it might have already been answered, it got annoying sifting through the 89/91 and redcy nonsense.
This was the easiest link, went 2000-2009: http://blog.philsteele.com/2010/07/10/conference-bowl-rankings-past-decade/
B10 was 28-41, 6-11 BCS. B12 was 38-39, 6-9. Obviously Nebraska has switched sides now, confusing who gets to count what, but I think wins stay within the conference they are earned.
Looks like since then it is B10 (17-26); B12 (18-20), obviously Ohio State won championship, and the SEC won the rest. Mich State beat Baylor in the only matchup last bowl season. KState beat Mich the year before.
As I said previously, I would love to switch SOS, but no way am I switching the opponents. B12's ranking was not better than B10s last year. Ohio State and Michigan State were top ten, as were Baylor and TCU, we know where they ended up. Then Wisconsin and KState were ranked top 20. Nebraska and Minnesota got votes, so did Oklahoma.
B12 went 5-30 vs ranked teams last year. Sure, call out Iowa for not beating winning teams, but the B12 was not good vs. competition, especially within their own conference.
One of the reasons I like "my" conference and wouldn't switch: B12 teams gave up, on average, 30 more points than B10, 4 basically gave up 400+ points, one did that in Big Ten. 4 in Big ten gave up 200 range, only TCU did for B12. Different conferences, different styles.