For the measurements they are comparable to DW ( if you use a DW4 go with K&G4), don't use the tables on their site, they are smaller than a measure or two. For the sound I would say that there are no differences between gold, rose gold and silver: I prefer gold because it feels smoother on the lips.
2007 Besson Prestige 2052, 3D+ K&G mouthpiece; JP373 baritone, 4B modified K&G mouthpiece; Bach 42GO trombone, T4C K&G mouthpiece; 1973 Besson New Standard 3 compensated valves, 3D+ K&G modified mouthpiece; Wessex French C tuba, 3D+ K&G modified mouthpiece.