My girlfriend trained for her first marathon while I was training for my first century (they were 2 weeks apart). Our training investment was very, very similiar. Our end result was very, very similiar. We both finished in respectable times and we were both able to walk the next day. Neither of us was shooting for speed or performance...our goals were to finish in relative comfort.

The century I trained for was similar to yours at about 5000 ft over 102 miles...which I would consider an 'average' century. A flat century would be less elevation, and a mountain century would be at least double that. Of course, weather is a huge factor, too....as you mentioned.

Anyway, my girlfriend is a runner and greatly dislikes biking. To her, a century is much, much harder than a marathon. I am a cyclist and I dislike running...to me, a marathon sounds WAY harder than a century. It's all about perspective.

I will say that when I tell people I do centuries, they are usually way more impressed than they should be. It's a challenge, no doubt about it, but completing one is not the end-all be-all that some people make it out to be. And, it's different for everyone. I know a guy who finished a century last fall after only riding for a few weeks. His longest ride ever was 44 miles and he did 100 hilly miles at a good pace. Granted, he was barely able to pedal across the finish line, but he completed it. I know others who trained diligently for weeks and who had to bail on that same century...so it really varies.

Now, if you asked me this question 2 years ago right after I first started biking, I'd have told you that a century was a crazy goal and only the most psycho of cyclists even attempted it...so again...it's all relative!