I can definitely relate. I climb with a wide variety of people from much less fit to much fitter, and on any kind of day where altitude is part of the challenge, my speed almost always takes way more of a hit than my partner’s. I’ve finally admitted that it’s something that is worth devoting time to improving, which is frustrating since legitimately high altitudes do not figure into even medium term goals for me. But despite making a lot of progress in fitness and fat adaptation the last few years, I haven’t seen much improvement in altitude tolerance.
It would be great to have more ideas (in particular that ^ video would be amazing) but my understanding is that increasing the number of times you’ve acclimated to a given altitude is a great way to improve your acclimatization for future trips to that altitude. While it’s not particularly appealing, planning trips whose primary goal is acclimatization training rather than skiing or climbing something interesting is as far as I can tell a thing that people do.
I live at sea level, and my immediate goals aren’t much above 4000m, so for me I’m just scheduling trips to Colorado. This makes me cranky, since climbing-wise I would much rather hang out in Canmore than Ouray, but hopefully it will prove worthwhile. It sounds like you’re well adapted to 3000-4000m, but trying to go to 6000m. Trips to 6000m are of course much more expensive and time consuming, but it seems possible that several years of 6000m trips (maybe going a week early to acclimatize before your likely more genetically advantaged partners) might make a big difference to trips in future years. And at least for me it has helped my motivation to admit that I’ve tried the I’ll-just-tough-it-out approach long enough to be pretty darn sure the end result will be a good chance we’ll have to bail because I suck at altitude.
I tried to fix a link and it seems to have instead deleted the post, so apologies if this shows up twice.