Curry 6 BBC vs Kelly 5C
The Kelly 5C has a wider cup diameter, the Curry 6 BBC has a larger throat opening.
Cup Diameter
The Kelly 5C has a cup diameter of 16.76 mm / 0.6598 in compared to 16.71 mm / 0.6580 in on the Curry 6 BBC — a difference of 0.05 mm / 0.0018 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 Curry 6 BBC has a wider throat (4.06 mm / 0.1600 in vs 3.80 mm / 0.1496 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Material
The Curry 6 BBC is described as unspecified, and the Kelly 5C as Lexan polycarbonate. 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.