Mark, I am going through something similar with my GR66MX ( deeper and more rounded cup)and my old "go to" Bachs" ... 1C,1 1/2c's ... my tone is so much more mature on the GR though. I really think the deeper cup affects the endurance ... but that is just my gut. I am banking that as my chops continue to build up the difference will be less. So I pretty much just play the GR. If I had to play a performance and felt my endurance would be iffy I think I would fall back on the Bach ... but I don't have to ...thankfully.