So I've been moping about this altitude thing since Sunday and it's taken me this long to realize that I had set myself up to fail (even though I actually did get up and back down the peak in mostly one rather miserable piece.)
It was a training hike and an experiment. I deliberately pushed my pace just to see what would happen, to find the limits, and I know from experience (which I had conveniently forgotten) that if I over-exert, I run out of oxygen and funny how everything stops working right then. This doesn't explain my difficulty on Shasta, but that may have been slightly incorrect training (or training that more included having to life my entire body weight.)
Being able to climb is fun and I tend to get carried away and go faster than I probably should. Part of the issue is that I tend to climb slower than others so I was enjoying being able to climb faster, and was trying to prove to myself that I could do it. (Sure, for a little while.)
It's tempting to redo the first part of the hike at a more moderate pace and see if I hit the wall at 7500'. My guess is that while I would probably slow down around that height, it wouldn't nearly be so dramatic. In particular, I should avoid forcing my muscles to work anaerobically (where they burn) while climbing as that may have been a factor.
Mostly I really need to stop persecuting myself about this. It's a challenge, not a character flaw - geez lighten up. I started to slip into the "Woe is me I never get to have things that are really important to me." Which is so not true.
This is all on hold till October as this Sat is a Wombats ride and the rest of the weekends in Sept should be spent prepping for our wedding.
Even though it may not help me much I am going to get an oximeter, as I love having hard data (like a heart rate monitor), and I judge myself less.