Michael - Good to see you, too! Thanks for the welcome back.
Ian and Andrew could confirm this, but I think the M-80, M-80 HP and M-100 would sound pretty much identical, with the M80 HP having about 3 dB more output below 160 Hz than the M80, and the M-100 having an additional 3 dB in output below 160 Hz than the M80 HP.
When we get back from vacation, the trigger will be pulled on the speakers - right now, the KEF Q900 is the front runner for the comparison. It's about the same $$$ as the M80, and is listed as a class "B" in Stereophile's recommended components.
Class "B" has speakers up to and over $10,000 per pair, so this is high praise from Stereophile.