I sell my mark VI alto last year and now I back play alto sax, soo I buy one conn 6M gold lacquer 275.XXX.
Great sound and fat, warm, but I always play meyer mouthpieces in alto sax, and it play good but no great in 6M for me.
I use one meyer 6M made in USA very old, nice and great control and tone, but I fell I need more things ... I have 3 meyer edition limited in past and its wonderfull player in all sax I play mark VI, SA I and II, SBA, BA and conn 6M too.
I prefer alexander superial 2 1/2 or 3 reeds, but play good with la voz, heemke and java green reeds too.
Well, let me know the best mouthpiece you play in conn 6Ms.