The XD is the deepest cup offered by Warburton. It is deep, but nothing out of the normal. It has a dark sound, but still trumpet-bright, especially in the high notes. It produces a clear, round, singing sound. Because of the small diameter (#7), the sound is quite small, but it is nice for a small ensemble. Not recommended for orchestra or marching band. The high notes require a lot of air pressure, but they are in tune, which is rare for deep mouthpieces (usually the high notes tend to be low with very deep cups). All in all, a very good, specialized cup.
Warning: Warburton cups seem to have the same depth irrespective of rim diameter, so that, for the same cup depth, it feels shallower the bigger the diameter of the rim.