Damn, I have a gig tonight and would very much like to do it with the new firmware, is it reasonably stable?
Also, I've dialed down the highs on many of my rigs in order to control the fizziness, do I need to raise them back after switching pure cab on? Mind you, I won't be able to give it a try until I get home at the end of the day, that's why I ask, so I can plan ahead.
Pure Cabinet will almost certainly alter your tones drastically. I would avoid temptation, upgrade after the gig and dial it in for the next one, it'll be worth the wait.