Bach 5C vs Stork CM3
The Stork CM3 has a wider cup diameter.
Cup Diameter
The Stork CM3 has a cup diameter of 16.30 mm / 0.6417 in compared to 16.25 mm / 0.6398 in on the Bach 5C — a difference of 0.05 mm / 0.0020 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a medium cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
Throat diameters are essentially identical at 3.66 mm / 0.1441 in, so resistance feel will be comparable.
Finish
The Bach 5C is listed as unspecified, and the Stork CM3 as Silver plate. Finish mainly changes lip feel, tarnish resistance, and appearance rather than cup geometry.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.