Back when I bought my M80s, I was able to directly compare various speakers at the Axiom factory. There was a subtle but noticeable difference between the M60 and M80 in the midrange and treble.
It was something you could hear if both speakers were on a switch, but if you listened to one in one room and then the other in another room, you would never hear the difference.
At the time, the difference between the two was about $400 and I decided the difference was worth it for me.
I think you will be happy with either speaker, so I guess it depends what you want.
