Marcinkiewicz 3 / 5C vs Monette Cornet C4LVS
The Marcinkiewicz 3 / 5C has a wider cup diameter, the Marcinkiewicz 3 / 5C has a larger throat opening.
Cup Diameter
The Marcinkiewicz 3 / 5C has a cup diameter of 17.20 mm / 0.6772 in compared to 16.20 mm / 0.6378 in on the Monette Cornet C4LVS — a difference of 1.00 mm / 0.0394 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
The Marcinkiewicz 3 / 5C has a wider throat (3.73 mm / 0.1469 in vs 3.66 mm / 0.1441 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
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.