Rankings are based on averages for the current members of the conferences over the past three years. I looked at two metrics: Sagarin Ratings (Performance Based Algorithm) and Football Attendance. The first set of rankings are based on the conferences as they currently exist. The second set is based on the Big 12 adding Memphis and Cinci.
Sagarin Average Team Ranking:
#1 SEC - 81.65
#2 Pac - 78.81
#3 Big 12 - 76.93 (without expansion)
#3 Big 12 - 75.81 (with Memphis and Cinci added)
#4 ACC - 75.05
#5 B1G - 74.78
NCAA Official Average Home Attendance
#1 SEC - 77,333
#2 B1G - 66,507
#3 Big 12 - 58,116 (without expansion)
#3 Big 12 - 54,094 (with Memphis and Cinci added)
#4 Pac - 52,734
#5 ACC - 50,046
We can add Memphis and Cinci and it will not significantly water down the quality of the league (at least not according to Sagarin) in comparison to the other conferences. There additions will also not have a significant impact in terms of average game attendance.
Sagarin Average Team Ranking:
#1 SEC - 81.65
#2 Pac - 78.81
#3 Big 12 - 76.93 (without expansion)
#3 Big 12 - 75.81 (with Memphis and Cinci added)
#4 ACC - 75.05
#5 B1G - 74.78
NCAA Official Average Home Attendance
#1 SEC - 77,333
#2 B1G - 66,507
#3 Big 12 - 58,116 (without expansion)
#3 Big 12 - 54,094 (with Memphis and Cinci added)
#4 Pac - 52,734
#5 ACC - 50,046
We can add Memphis and Cinci and it will not significantly water down the quality of the league (at least not according to Sagarin) in comparison to the other conferences. There additions will also not have a significant impact in terms of average game attendance.