Having been involved in the Blind Listen Testing of all these models I can say for sure the biggest upgrade in the sound quality comes with the wholesale changes to all the models (the family of curves
http://www.axiomaudio.com/blog/the-family-of-curves/ ). So M100s would definitely sound better than your M80s, but M80s made today will sound better than your current ones also. The current M100 does win the Blind Listen Test against the current M80s but the delta, outside the bass region where the difference is substantial, is nowhere near as large as between an older M80 and a current M100.
The LFR1100 is an interesting animal. I think the best way to describe it would be a like a discovery of some new pleasure; once you experience the LFR1100s there is no going back. And interestingly the difference from an M100 to an LFR1100 is at first seemingly small, the tonal balance is identical so there is no difference that way, it is the big 3D soundstage that exists everywhere in the room that gets to you and then there is no going back.
