Altitude is not detrimental over 600m, I’d argue it may be a hair beneficial. Source: sitting in Albuquerque right now.
I disagree, and so does the NCAA altitude conversion (for 800m, I didn't find one for 600m), which is based on a lot of data. I trained in Albuquerque and found a big impact for anything aerobic, and even the 600m has a big aerobic component--800m even more.