I might be shooting myself in the foot.. but...
With this update, the MV received a significant change. Consider this: With a tube amp that has a Master Volume, there will still be a "sweet spot," and for some/many amps, it is still when the amp is cranked up a bit. Not dimed, but still running hotter than I experienced with pre4.x.x. With 4.x.x, I can now treat the MV more.. "realistically." IMO. So, if I run my MV up around 1-2 o'clock now, it is not.. "causing a harshness that was there previously." That is a all-inclusive, ball-park statement that some/many may disagree with. It is my experience.
So! Because a tube amp is very interactive.. turn one knob, and the relationship between it all changes (such as.. tonestack range, etc).. I am not sure a definitive "MV @ 3.5 previously = 5.45 now" &guide* could even be put out there. Well, at least not reliably. IMO. I guess maybe.. compare it to sending your amp out to get some component values changed; your old "values" would no longer be relevant, and figuring out a formula of some sort to simulate those old settings would be difficult to highly improbable IMO.
For some, it will "suck." Look at the Digitech 2120. It is what it is, and no changes are forthcoming. You have a Constant, not a Variable; but, that is something you really do not have a choice in. You buy it, you should know that ahead of time. As Mike Brady might say, "Caveat Emptor." On the other hand, you have different fingers. And with the Axe-Fx II, you have a product that is still being actively.. enthusiastically!!!.. being developed. Ver3 firmware will work just fine. I have pieces of software that I will not update until I see what happens with more recent versions. Heck- Pro Tools is so borked with the latest version that I have no plans to upgrade anytime soon, even if it were free! Point is, Cliff/Fractal do a great job with warnings, and if a release says it will alter the sound, it is something to consider. It can be a lot of fun to ride the front of a wave, but it is also the spot that can pull back just enough to drop you face first into the sand.. and then pound you (nearly) to death as it rolls over you. It can be really difficult to NOT want to ride that wave!!!