The measurements look very close but the profiles behave differently, and yes, there are gamut differences between them, but tends to be small. For example if you are using a paper containing an OBA and you make an M1 and an M2 profile, the M2 may have a slightly smaller gamut than the M1. In terms of profiling accuracy, which to my mind is a bigger deal than small differences of gamut, it is best to select the correct "M" relative to the paper at hand - does make some difference.