Chris, there is no comparison between M80v2 and M100v4. Take it from someone who has owned both. Properly placed, the M100s will give you soundstage depth and width and imaging that is simply not possible from your M80v2. They are simply better throughout the entire frequency range and have addictive mid-bass and mids.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated