Re: mouthpieces for a Mark VI....
I've been playing a Guardala on my Tenor for some 20 years. It is one of the older hand made ones, the 'Traditional' model. I stopped by Dave's shop in New York and tried a bunch. The Studio played great, but was too darn bright for what I wanted. It would work perfectly in a really loud band.
I don't think that anything quite like the 'Traditional' is made anymore, large bore, fairly large opening and a fairly low baffle. I felt the gold plated one sounded smoother and a bit darker, so I spend the extra and bought that.
It wasn't cheap, but it sure works well.
You may be able to find a used one floating around.
I've never tried any of the laser cut newer models, so I have no comment on them.