You need to be talking to the Indians. They commonly ride to elevations higher than 10,000 feet, although it's usually on 350s. Those guys usually changed jets once on the rides to 17,000 feet at about 11,000.
I have ridden several CV carbed bikes to 8000 on the Crest and they do alright. The GB500 worked great up there.
Quite honestly, you are really making too much out of the whole thing.
When you get the carb set right for 2000 feet you really won't have any trouble going up the mountains. My Amal equipped Nortless (Matchless) did fine up there. Yes, you will lose power, but I don't care waht kins of carburetion or FI you have, it's going to lose power. I have never fouled a plug up there in 30 years of riding these mountains. I have had bikes that were jetted too rich at sea level stumble occasionally at high altitudes, but they keep on truckin'.
So don't worry too much about it, just get the jetting right for 2,000 and it will easily handle any of the altitudes around here. If you get up to 10,000, it will probably still be OK, If not, change the main jet. No Biggie.
You guys out there really put to much worrying about the abilities ofthese carbs. If all the parts are working properly, the carbs are to going to go wicky-wack in one session. And certainly the jetting isn't going to up and stop working if it's been working for months or years. Very few running problems are carb related. Or if they are, they should be quickly found. they are usually found in; clogged idle air holes, crap in the float needle, sunken floats, main or needle jets coming loose, needle clips falling off, and if it's an old slide, worn out. Here can be come secondary spots like the enrichening circuit being worn out, but those usually let you have some early warning.
In trouble shooting your bike, start with the last thing you worked on!
Bare