I just got back from a week in Colorado and did my first true climbs. I was in Frisco and rode the casual stuff in the valley between Dillon and Breckenridge. I'm not gonna lie... I didn't dare attempt Hoosier Pass. Two problems with it: no shoulder most of the time, and intermittent monsoon rain. I'm a flatlander and I'm not taking my chances descending an alpine climb in the rain.
The first 24 hours was brutal since Frisco is 9,000 feet and Wichita is 1,500. After 48 hours I felt better, and by the end of the trip I was relatively but not totally fine.
The climbs I did do were manageable with proper pacing. They were not 8% for 4.4 miles, which I'm pretty sure is Cat1 or HC if you are not exaggerating, but I did several shorter cat 2 and 3.
I used a 50/34 and 11-26 drivetrain. I actually had an 11-32 cassette but found to my displeasure that my bike has a Rival short cage, not medium as the build sheet from CC says it should have.
However, it was a family vacation and my 62 y-o father in law needed the 11-32 more than me, and it worked great on his Apex-equipped bike.