Great horn, Matt. I wondered who had ordered the 6/4 silver Rodolf Meinl BBb when I placed my order last winter for the 5/4 Bayreuth BBb. Both of our horns are pictured in front of Lee Stofer's garage just after he received them:
http://www.gwwilk.com/tubas As you can see, they are almost identical through the valve assembly, but the 6/4 is about an inch or so taller due to the larger bottom bow. It looks like the factory curved your leadpipe down about an inch in order to give the 6/4 approximately the same playing height as the 5/4.
I, too, have a Bayamo mp and I like it a lot. And oddly enough my other BBb tuba is a St. Pete! The Bayamo makes the St. Pete sound like a completely different instrument, and articulation seems easier on the Bayreuth with the Bayamo. I keep switching around and experimenting with the RM1, Bayamo, Kellyburg, and a Roger Bobo Solo replica. Each seems to have something just a little different to offer.
Your difficulties in finding a comfortable playing position also ring true. I'm 6' 1" tall, but opposite the 'gorilla' build of some other tubists who frequent TubeNet in that I'm long legged. Hence I prefer a taller seat than the 'gorillas'. I also bought a K&M playing rest shortly after I received the Bayreuth because my DEG wasn't holding up very well under the strain. Because the K&M playing stand won't adjust low enough to use an ordinary chair I first bought a drafting chair in order to boost my height. This worked, but it was just a bit too high and I couldn't quite sit erect because the playing stand was just a bit too far forward. So after seeing a thread here on drum thrones I bought a Tama Ergo-Rider Quartet drum throne from WWBW. It's perfect in that I can position the Bayreuth where I want it on the K&M stand and also get some back support during playing.
So, I have this large instrument, a playing stand, and a special chair that I might have to cart around if I were playing gigs. In reality, I'm just practicing right now, but if I need to travel I found a cheap 22" x 18" bass drum case on ebay that will hold the stand and the drum throne, both of which are portable (plus any necessary refreshments!)
Best Regards,
Jerry