Here is the story. I live in Wisconsin. It's relatively flat here. I'll be racing in Colorado this summer at Norba Nationals in the XC event.

http://www.snowmassnational.com/

Here is a map of last year's course. Note the elevation is ~8500-10,000 feet with 1400 feet of climbing per lap.

http://www.snowmassnational.com/XC.htm

Needless to say I'm worried about being able to breathe. I'm interested in hearing experiences about racing at altitude.