I know nothing about CO singletrack, but as flatlanders, DH and I struggled a bit on a recent mountain bike trip to Canyonlands in Utah at 5k feet. How hard do you anticipate it being riding for you to ride at 9k+ feet? I would, in the very least, give yourself some time to acclimate to the altitude before embarking on the ride and recognize that it's likely going to be challenging aerobically, even if the technicality of the trail itself is okay for your skill level.