Auburn's defense the past few years has had more to do with talent than Chizik. Auburn has recruited phenominal talent and speed on the defensive side of the football, as that is usually Tuberville's top priority in recruiting, being a former DC himself. Not discounting Chizik, he has done a great job at Auburn. But look at the talent AU has had in the past few years. Torbor, Dansby, D. Thomas, Rosegreen, Rogers, etc.
Chizik is definitely a good pick-up for Texas, but I don't see him making a huge impact next season. Vince Young will probably have more to do with longhorns winning next season than anything else.
In any event, he will be gone as soon as a head coaching job comes open. He has big aspirations to be a head coach eventually.