In the same amount of hunting time an M6 is likely to produce more good targets in dry sand than a standard MXT. The M6 is quieter but the feature that gives an experienced user the advantage with an M6 is the tone ID.
The situation changes when the operating features of an MXT Pro are compared to the features of M6. The MXT Pro has the option of using the same tone ID as the M6. And, the MXT Pro Threshold can be adjusted to just below audible and function like a silent search machine. In other words, an MXT Pro can be adjusted to operate like an M6. An M6 has no feature that cannot be duplicated by an MXT Pro.
An MXT Pro has many features not found on an M6 such as:
Display backlight ... a big feature if you do any night hunting.
Ability to lock the detector in all metal pinpoint mode.
Single button Ground Grab.
Audible Threshold so you can hear those deep whisper signals.
Two Relic search modes with different SAT speeds.
Prospecting search mode.
An M6 is truly an outstanding coin and jewelry hunting machine. However, in my opinion, it simply does not have the range of features and capabilities of the MXT Pro.