I can tell you, the difference in oxygen is real. After living here, training here, it's noticeable for at least 48 hours.
The bonus is when you head down to sea level, the first 24 hours are like someone caffeinated everything you ate and drank. I ran sub 7 minute miles in California after running about 9 minutes in Colorado. It's real.
Knowing that, the strategy is to rotate your players as much as possible. Regular substitution patterns don't work up here.