I've never owned the m100 but if it helps, I've auditioned it heaps prior to buying the p7. Owned the momentums over ear previously before and was not satisfied with the bass as it had rumble but doesn't go really deep plus feared the headband would get bent. M100 seemed almost the same with less rumble but the build quality is really excellent thus really considered it..but P7 has better and deeper bass plus overall clarity, scales better/well w amplification/volume and is more musical. M100 could be more linear though, but I don't really go for true linear.. Just play by ear
build quality you get real leather instead of fake leather on the m100