If your definition of Mcrit is where a shock forms anywhere on the airplane, then I can't help you.
I don't think anyone else can either unless they have a set of surface pressure or velocity distributions for the wing, body, horizontal tail, or nacelles/struts.
In cruise, you can have a shock in the vicinity of the cab maximum curvature areas before any form on the lifting surfaces.
Another potential place is the nacelle/struct/wing junctures. More than one airplane as come to grief because to enough attention was paid to this area.
You also shouldn't neglect the low speed flight arena. Shocks can be present on slats as the airplane approachs a stall.
In summary, shock formation and drag rise isn't only a function of airfoil technology and wing sweep.
To answer your question in terms of approximate LRC Mach:
737 Classic .74M to .75M
737 Next Gen. .80M
MD80 .76M
A330-300 .82M
A340-300 .805M
Since the last two have the same wing, do you have any guess as to why the A340-300 is slower?