I'll close out my own thread...

IMHO, the M80's are better. Hard to A/B compare them, different components, etc. But I can say that at least for me, the M80's bass isn't quite as pounding - but it's nice and smooth. Im the midrange, the M80's seem more accurate and cleaner. Highs are significantly better on the M80 - nowhere near as bright as the RS100's. Happy with my choice to go M80!

M80v2 | VP150v2 | QS8v2
SVS Pci+ 20-39
Emotiva UMC-1 & LPA-1
M22ti + T-Amp, in the Office