It is not possible for UGA's defense to have a big game against Auburn. This is because Auburn's offense is so bad, that shutting them down really doesn't prove anything. Even if we shut them out and win, say, 28-0, it really doesn't say anything about our D, other than it's decent enough to shut out a team that won a game 3-2.
On the other hand, it is entirely possible for our D to prove that they're not any good against Auburn. If the Tigers score more than 14 on us, it will be more ammunition for the fire WM crowd.