Kelly 5C vs Yamaha CR-16ES-GP
The Yamaha CR-16ES-GP has a wider cup diameter, the Yamaha CR-16ES-GP has a larger throat opening.
Cup Diameter
The Yamaha CR-16ES-GP has a cup diameter of 17.05 mm / 0.6713 in compared to 16.76 mm / 0.6598 in on the Kelly 5C — a difference of 0.29 mm / 0.0114 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a very deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Yamaha CR-16ES-GP has a wider throat (3.98 mm / 0.1567 in vs 3.80 mm / 0.1496 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Material
The Kelly 5C is described as Lexan polycarbonate, and the Yamaha CR-16ES-GP as unspecified. Material affects mass, warmth, and how quickly the piece responds.
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.