I don't know. It's not a fair measure, as all bowl opponents are not created equal. Oregon State's victory over the Domers, for example, isn't as impressive as Texas beating Michigan.
The Mountain West finished at 2-1, so I suspect they will have the best percentage.
If Texas beating Michigan is impressive (with that partially blocked field goal scraping paint on the cross-bar!) is Notre Dame beating Michigan this year impressive to you? And for that matter, is Notre Dame beating Tennessee at Tennessee impressive too?