This is something I've thought about a lot lately. I began playing in the 60's and that was the way it was presented to me. Selmer was the only pro horn worth having, or so it was said. This is not intended to be a knock against Selmer because the Mark VI was indeed a fabulous horn. However, because I was steered toward a Mark VI I never had the opportunity to try anything else and had no idea how good some of the other makes were. One example is the King Super 20. That wasn't even on the radar back then and yet, as I know now, the Super 20 was a fantastic horn. In fact, I never had the opportunity to play one until very recently. After spending an hour or so playing a 1965 Super 20 I bought it on the spot. Just my humble opinion sprinkled with a generous helping of subjectivity but I like it better than any Mark VI tenor I've ever played and I've played a lot of them. When I was in High School there were a couple of kids that had Buffet Super Dynactions and we sort of looked down our noses at them as if somehow they had settled on a lesser horn and should've insisted that their parents buy them a Mark VI. I never actually played any of their horns. It wasn't until I was grown up and playing professionally that I had a chance to play a SDA. I never actually bought one but have played several of them and they are super good horns. I never even heard of a Keilwerth back in the '60s. Turns out Keilwerth was building some of the finest horns in the world back then. Who knew? All this to say, although there is no doubt the Mark VI was a very special instrument, I can't help but wonder why so many of us never even considered any of the really fine offerings from other manufacturers. My parents bought me a Mark VI in 1970 and I can't thank them enough for it but I wonder if that's the horn I would've chosen had I had the chance to evaluate it against a Super 20, a Super Dynaction and maybe and H. Couf Superba.
Oh, and so as not to highjack the thread, yes you can definitely feel and hear the difference.
