124, to be honest, I don't know much about the M100 series. During my time in the jazz organ trio heyday, none of my fellow organist had or used spinets, only B3's with a rare C3 (or sometimes a modded B2,C2,BV,CV with aftermarket-percussion) but never a spinet (ruined their image I suppose ). Plenty of M3's on the Rock scene however, but that was a decade later. From what I've heard, there was a noticeable difference in the vibrato section and also in the preamps, but I'm not sure how that effected the overall sound.

chas