Hey Gene
I had the same thought, but upon further research realized that most residential breakers are actually not upgradeable. Most residential panels are plug-on type, and there is only one breaker from the same brand that will fit the panel.
Mikeeastman is using rail mount breakers in his audio subpanel, which allows different width breakers, and his brand, Square D, offers 2 quality levels of breakers QO and Homeline (of different widths) that both can be used in his rail mount panel. If he had a plug-on Square D panel he could not do that because every plug-on panel requires specific width breakers.
I have Cutler Hammer panel, it has 3/4" plug in breakers. I have the old Cutler Hammer tan colored breakers. But since mine was installed Eaton bought out CH and now the black handled Eaton breakers can replace the old tan handled CH breakers, but most of what I read claims they are not as high quality as the old CH breakers which I already have.
If there was a particular breaker that was worth upgrading to, you'd need to install a new subpanel that would fit the breaker you want to use. But then you have an "unworthy" 50A breaker in the main panel that feeds the audiophile subpanel, so are you any further ahead? A "worthy" breaker in an audio subpanel doesn't reduce whatever impedance was added from upstream breakers, it can only minimize the impedance it adds. The plug on feet connections add impedance too.
I think I have a parallel outside panel at my meter that has big breakers for a gaspack and a compressor. Since they are such high current loads makes no sense to run long lines just to have the breakers in the main panel on other side of the house. I'd like to stick a 20A audio breaker in the parallel panel as it's only 20 feet from my stereo, then I could afford a short run of JPS romex ($25/ft) which does make a noticeable difference. Not sure how feasible this is, but at least the parallel panel is already installed and signed off, as parallel panel relies on an exception rule to NEC, so I might not get a electrician to attempt to get a new parallel panel inspected just for a couple of 20A receptacle for a stereo. Not important enough to invoke NEC exception. But the parallel panel is tan also, so it's Cutler Hammer breakers.
I'm certainly no expert on this breaker thing, I only know what I read on the web yesterday, fwiw. I hope Mike can shed more light and correct any of my errors. It's tempting to upgrade what we all view as a potential bottleneck.
It seems to me that no matter how awesome the breaker, you could always improve it by buttering the contacts and feet with a little SST. That should work with any breaker. I don't know how easy it is to get SST into the contacts, if possible at all.