Bach 6½AL (large shank) vs Schilke 59
The Schilke 59 has a wider cup diameter, the Schilke 59 has a larger throat opening.
Cup Diameter
The Schilke 59 has a cup diameter of 28.52 mm / 1.1228 in compared to 25.40 mm / 1.0000 in on the Bach 6½AL (large shank) — a difference of 3.12 mm / 0.1228 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Schilke 59 has a wider throat (7.54 mm / 0.2969 in vs 6.63 mm / 0.2610 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.