I've done quite a few metric centuries - there's another one on this Sunday as part of our local Grand Slam series (about 160K all up). There's an 80 k option, which is what I'll probably do as the rides tend to be fairly hilly, and I just CAN'T do hills. I'm better at it than I was a year ago, and I go out trying quite often. I figure the only way to get better at climbing hills is to go out and climb hills. I read about technique, breathing, nutrition, dehydration, gearing etc etc ad infinitum. But nothing works. I get to a certain point, there's nothing there, and I have to just stop and walk it. So until there's a century that isn't climbing, I'll be a metric century rider.