This isn't empirical...
...but I agree with flab. I think the gap has widened. I always knew we were an underdog in the late 90's early 2000's under Sherrill. But I also felt like we could win. I never thought, there's no way. Now, when we play LSU & Bama, I don't feel there's chance we win outside of their whole team falling in a sinkhole. For comparisons sake:
'00 vs. West (Auburn) & East (Florida) champs, we won against both (Lost to LSU by 7)
'99 vs. eventual West champs @BDS (Bama), we held our own, could have won, but lost late (beat LSU)
'98 vs. eventual national champions in the SECCG (Tennessee), we held our own, could have won, but lost late (Lost to LSUby 35)
'12 vs. eventual national champions (Bama), we get our doors blown off (Lost to LSU 20)
'11 vs. eventual national champions (Bama), never in doubt loss (Lost to LSU by 13)
'10 vs. eventual national champions (Auburn), played them closer than anybody all year (Lost to LSU by 22)
Other than playing Auburn close, we haven't threatened a top team yet. Whereas, in the Sherrill years, we threatened and beat them frequently. I think we're better now talent-wise, or at least close, but the whatever our marginal improvement level, the big boys' margins have improved even more...