I find the M110 which i just got, to have a little narrower heel pocket than B10, besides being slightly narrower in the forefoot.
The B100 being the top of the line in that series, comes with the custom pro liner, while the M100 being one step down in that series, comes with the custom sport liner, which is a step down from the pro liner. The M110 does come with the pro liner though.
Some other differences are that the B100 has the 3D adjustments on the cuff while the M100 has a little less versatility in it's adjustments.
I would say buy whichever one fits you the best. I've skied the respective new b10 the last two years, but I'm moving to the m110 this year trying to get a little better cuff fit and maybe a little more performance. I may have to do a little grinding though. The B10 skis well if it fits a person. Later, Ricb.