When I first joined Axiom around 2002, I didn't much like the M80ti -- it sounded harsh on brass instruments and some female vocals, also a bit sibilant (unlike the M22ti, which I loved from the very beginning) -- and I urged Ian to tweak the M80 crossover and smooth out the midrange, which he did. Even while it was still designated "ti", the "new" M80ti became a wonderful speaker to my ears in double-blind tests. That change occurred a year or so after I joined Axiom, and awhile after that the v2 version replaced the "ti" designation.
Further improvements in the tweeter and drive units resulted in the v3, which delivered a deeper and more spacious soundstage. I've not heard the v4 M80, so I can't comment on it, but I expect there would have been small improvements to an already great loudspeaker.