I used to bike to work a few times a week, an easy five mile ride to my old office. One year after giving blood (not the same day but definitely the same week), the ride was awful. It was almost painful. I'm at about 900-1000' above sea level here, and that memory is surprisingly similar to how I felt hiking at 10,000' after living my whole life at 1000'.The experience was very similar to attempting to run at 7200 feet having been acclimated to sea level.
It stands to reason. Give a pint of blood, knock out 12% of your oxygen transport capability. Go from 1000 feet to 4000 feet, you go from 20.1% oxygen to 17.9%. a thousand feet to ten thousand feet is taking you from 20% oxygen to 14%... that's a 30% hit. Probably not quite like giving up three pints of blood, but also not like shotgunning a Red Bull either. Had you driven there you would have noticed your car sucks, too. We knew from dyno tests that a normally-aspirated motor makes about 75-80% of the power it would at sea level. I built a full-roller V8 and drove it to school. It broke in about Utah and went from "satisfying" to "fun." Coming down out of Snoqualmie pass it went from "fun" to "oh holy shit I've built a monster." I probably gained 200 HP in 1500 miles.
Yup, those numbers look about right. Can't wait to run a 50k at 6,000ft...