Shane, do me a favor.... Before you do the update, record a DI track, and then re-amp it in 2.11 software with any preset or cabs you may be interested in.
Then after you update to 2.12 you can re- amp it again with the exact same preset or presets and test it against the 2.11 re-amp.
Basically what it boils down to is playing the two re-amped tracks at the same time and flipping the phase on one of them. If the sound cancels out and you hear nothing at all, then the sounds are the same, and the software has not changed from 2.11 to 2.12.
If after youve flipped the phase and you hear anything at all, then the sounds from 2.11 HAVE in fact chaged, and are different than the sounds in 2.12. To what extent is harder to say.
....and then if you just wanna be left alone to play guitar thats cool too ;)