Hi ATR,
If you want a 'ballpark' figure for Mcrit (ballpark but a pretty good one), Mcrit is typically at or slightly below the Climbing Mach Number. For example, if the aircraft climbs at M0.74 and typically cruises at M0.78, you can put your money on Mcrit being very close to M0.74
Cruise performance depends upon the point of tangency from the 0/0 origin to the drag curve, thus most economical cruise speed is typically a little above Mcrit (about 0.04 to 0.05). Climb performance looks at Power (not thrust) Available Vs Power Required, and therefore looks at the delta between the two, thus, best climb is typically very close to Mcrit (or slightly above it).
Best Regards,
Old Smokey