Late to this discussion, but I bought a 6CM mouthpiece recently for alto. I've been comparing it with a Rousseau Studio Jazz SJ6. (Before I go further I should mention that I play infrequently, some days I only have time to blow long overtones and a few riffs, and that's after a long layoff from regularly playing at all.) Those two mouthpieces may seem like apples and oranges -- the SJ6 has a bit of a baffle, while the 6CM has what I'd almost describe as an anti-baffle -- but what they do have in common is that they both "feel" better, and sound better (to me), than anything else I've got around.
For me, it's easier to hit the palm-key notes on the 6CM and the upper octave (A2 and up) just speaks out better in general. The SJ6, of course, has a jazzier (or somewhat edgier) sound, but I've found I can make the 6CM do this. I played both for my wife, who is something of a disinterested 3rd party (doesn't play an instrument; not into jazz). I asked her simply to decide which one she thought sounded prettier, which seems as good a criterion as any. She picked the 6CM over the SJ6. (A few days ago she picked the SJ6 over a Runyon 88 #6.)
Also worth noting, I guess, that the 6CM seems relatively open for this sort of mouthpiece (though it's still only .075" or so) compared with the 4C or 4CM that are, apparently, more common (and the plastic Cs have closer tips than the hard rubber CMs). I've also noticed that I'm happier with a slightly harder reed now, e.g. a La Voz Medium instead of a Medium Soft or a Vandoren Java 2.5 (which are what I used to use).
Might as well mention where my head and ears are lately, though: it's been larger doses of Benny Carter, Art Pepper, and Gigi Gryce, whereas when I regularly practiced before (15-20 years ago) it was a bigger diet of, say, Sanborn or Cannonball.
My $0.02.