At inception:
Big 12:
Colorado - AAU
Nebraska - AAU
Missouri - AAU
Texas A&M - AAU
Texas - AAU
Kansas - AAU
ISU - AAU
SEC:
Florida - AAU
Vanderbilt - AAU
Notice how many Big 12 schools have since moved over to the less "academically rigorous" SEC? I'm not discounting Altimore's arguments about the high value of research standing and academic cachet that is placed by the university president's when considering a move. History tells us in the Big 12 that is only a piece of the story.
Shared institutional profile, culture, etc. play a larger role in the decision making process. The PAC thumbing their noses at an R1 Baylor while simultaneously considering the R2 SMU and R2 SDSU, is extremely humorous to me when the argument comes down to "academic cachet".