In addition, im also worried about altitude sickness but i'd appreciate some firsthand accounts on how significant it is.
If you're in decent shape, you should be fine.
if you are in good health and work out you will be fine.
Just wanted to say that just cos you're healthy and fit, doesn't mean, that you're not prone to altitude sickness (healthy in terms of healthy lifestyle and not healthy in terms of not having an infection, which could
make you more prone). You never know in advance, who's going to be affected, predisposition is not yet known.
I know a completely healthy fit girl suffering from severe altitude sickness (incl. Edema) as low as 6500ft (she had to be emergency rescued by heli doing a simple recreational excursion).
On the other hand, when I did a trip to the Andes (14800ft), I expected me (asthmatic and long term smoker) to be the one of the group most prone, the other group members all being healthy and fit. I felt pretty well up there (sure, I was breathing holes into the air as well), but the most healthy gal of the group experienced altitude sickness and had to go down.
One of my bros friends just let me know that he has pretty severe athsma, at which point i was tempted to tell him "sucks to your asmar" but, I dont think colorado is a very good idea for him, unless we have no other options.
I don't feel any inconveniency boarding/breathing at 9900ft, while others without asthma already complain that they have to breathe hard - I use to joke that my lung is used to get along with little air
. I begin to feel a difference at 11500ft though. Being asthmatic hasn't prevented a friend of mine from doing touring at pretty high mountains. Asthma doesn't mean, you have to exclude destinations/activities per se. It depends, how well he can manage it.